I agree, scrollbars are too thin (and there are many Blender users who do think so too):
Scrollbars Design: ⚓ T69391 Scrollbars Design
UI Experiment: Scrollbars: ⚙ D6505 UI Experiment: Scrollbars
Indeed, thin scrollbars are a problem generally in Blender. Maybe it’s outside the scope of an outliner project. The reason I still wrote it in this thread is that the thin scroll bar has the largest negative effect on usability of the outliner. I mean it’s basically a long list, that scrolling through it should be easy is self-evident.
I think that filters popover should contain more filters per type.
In 2020, we should have new object types (Volume, Hair, Point Cloud).
Grease Pencil objects may be as frequent in a 2D animation scene than meshes in a 3D animation scene. But there is no specific filter that differentiate them from Curves/Paths, armatures, lattices.
I am not requesting a filter per object type.
But if you want to find a curve in outliner while continuing to see the whole scene in 3D view, that does not help to have so many things into Others filter.
I would add those filters
As is, Others filter would still correspond to Metaballs, Texts, Lattices, Speakers.
Can we please introduce groups so collections can finally be render layers. We need groups with own data block to move, rotate and scale everything as a parent of included objects. So far i can use empty to “simulate” groups but thats work around we need normal groups.
Great you see to continue this project, the last iteration was already a gamechanger and im looking forward to the results of this round:D
I was discussing some hiraries that would be possible for a project and we came across a scenario where it would be nice to be able to have a object as the parent of a collection. Is there something like this planned?
Just to have it in this thread as well. I think it was mentioned that this is supposed to be part of one of the main reworks, anyways, though. So just to spam it one last time 
Thank you very much for the continued improvement of the outliner. This is making a lot of a difference in daily work. 
Could be great being able to rename the next object by hitting tab like in a file explorer 
Maybe not splitting them up, but a different (colored) icon, or added link icon to the Collection.
I have to agree it’s a bit of a hit 'n miss sometimes when you have lots of them in your scene.
So you basically want the Softimage Pass/Partition workflow:
http://docs.autodesk.com/SI/2015/ENU/#!/url=./files/passes_WhatIsaRenderPass.htm
Which in my opinion already solves a bit of issues with Collections and rendering. Using the Collections for grouping things in the scene,. -and- rendering is not really optimal imho. Things can go wrong easily when scenes and render setups get more complex. Having some separation is already preventing this more.
Perhaps it is a little off target but when the collections were incorporated, it was said that the layers of the Armature would adopt the same system once it was tested.
Thanks for all the suggestions and feedback everyone! With 38 replies already, I think it would be silly to attempt replying to everyone, but I’ll try to make some good comments. I would also love more feedback on the main proposed goals I listed. I can clarify if needed, and I’ll add links to the development tasks to my original post after I post this.
@eobet and @jc4d you both mention highlights and active vs selected elements. The Mode toggle and activation column in my proposal plans to address this at least somewhat. I’m also currently fixing selection to make mode toggle, selection, and activation more distinct operations. Some good mockups of the current design are here: https://developer.blender.org/T68498. Also, shift+click on the triangles will expand/collapse all.
@AndrewPalmer I believe selection is working as intended. Ctrl+click to extend and shift+click to select a range.
We’ve had the “remove active state” debate last year but that is part of Blender and won’t be removed.
@radi0n I plan to clean up the context menu, but I don’t expect that to include adding more options. The idea for the context menu is to have some very basic general operations, alongside more hierarchical options.
@nokipaike That is a heavy scene. I tested and I think that the delay is not just within the outliner. Even a normal select has a slight delay compared to the default scene on my machine. Also, holding down the arrow key to scroll is not preferred when there is a scrollbar and mouse scrolling which don’t have the overhead of selection.
@silex I really think autoscroll with drag and drop could be cool as well. One issue I see is that you can drag and drop into the 3D view as well, and having the list scroll in that case might be annoying. You can currently scroll a mouse wheel while dragging and dropping though.
@Josephbburg You can disable non-object data. Look at the filter popover.
@xan2622 I’ve seen lots of suggestions for adding selected objects to a new collection, and I have already discussed it with my mentors. I am not sure yet if that will be default or an option, but it would be useful indeed.
Common Groups are planned for a long time, but they are out from this GSoC.
That could be solved by creating areas at the top and bottom within Outliner that can detect hovering with dragged item. If the hover time is less than let say a second that means user was dragging item outside Outliner and the autoscroll is not activated.
Yes, there are many ways they can be marked, separate lists is one of possible solutions, that have its pros and cons.
Amen to Alberto and hallelujah to EAW. This issue drives me nuts. For the life of me I don’t know why that wasn’t implemented in the first place. But, Blender is free so I’m not going to complain (too loudly that is…).
Rich
It is still uncomfortable for me that when you disable a collection (exclude from viewlayer), the elements of that collection disappear in outlener and you cannot select them or see their properties. It has happened to me many times that I need to see the properties of elements contained in a disabled collection, and having to enable that collection to see them results in an uncomfortable extra steps (sometimes you must enable more than one collection to try to find the item you were looking for).
Perhaps this, and when elements should be greyed out or not visible at all should be more discussed.
Since I think that the objective of Outliner is to be able to organize elements and layers, my personal opinion is that elements should never disappear from Outliner. Not visible or disabled for view layer elements/collections could be treated in different ways, for example greyed out text, strikethrough text, different colors, marks, etc.
@tintwotin outliner to sequencer drag+drop is likely simple enough to be an additional fix this summer (I haven’t looked, but it shouldn’t be too bad). I expect the modifications to the sequence view mode you described would be a larger project later on.
@thornydre while that would be nice, for now Blender doesn’t allow hidden objects to be selected
@RainerTrummer sorting improvements is one of my big goals for the summer, and the idea is to make the current sorting apply to both objects and collections, not the mixture of the two that currently exists.
@RonanDucluzeau A part of my plan is to improve sorting. When talking with my mentors we decided that manual, and alphabetical would stay, with maybe sorting by type as well. Maybe this could help find curves (as in your example) and not require a filter for each type.
@Manojlo I’m pretty sure collections and view layers were intended to replace layers and groups from before 2.80. You can make a collection instance, have you tried that? Also @kromar you could make a collection instance a child of an object.
That’s already tackled in the current 2.90 alpha branch if I am not mistaken. It is not backwards compatible, but it works as soon as you toggle states in a 2.90 scene, and is also saved with the file.
have you tried that yourself? first its very abstract to even start linking something to the same scene and then you will end up with a huge mess in the outliner for something that could and should be very clean.
So direct parenting of collections to objects is still something i ask for:D
On the sequencer thing. I think the drag and drop would mainly be useful if the Outliner, in Sequence mode, could show all scene names and the a/v content inside of them. Currently it only shows the a/v content of the current scene.