I don’t think there will be custom editor support in 2.80, it would be for a later release. The support for tabs in the N-key sidebar is new in 2.8, and I think the result then will be quite similar to the T-key toolbar in 2.7.
I don’t see how custom editors provide much of a solution to that problem though. For most of the add-ons it would not be convenient to have to open an editor rather than access them from the side of the 3D viewport. There are only a few add-ons where a new editor helps.
Some add-ons can be converted to active tools, which can help clean up the UI by only showing the relevant settings and tools in the topbar when the tool is active.