Well. There is an option for white wireframe in 2.80. It is called Show Wire.
It is at the end of Overlays popover.
Wireframe option with slider is global for all objects of scene.
Show Wire is just for active object under Weight Paint mode.
About categorization of brushes by tools and lack of shortcuts per brush, you are not only user unsatisfied by that. We complained about it for all paint and sculpt modes.
Take a look at discussion about tools/brush workflow thread :
The Tools/Brush Workflow
Sculptor and texture artist of Spring movie made a proposal to let user decide what brushes toolbar should show.
About an automatic switch to Solid display when entering weight paint mode, it may be problematic if weight group is not used for rigging armatures.
If it is used to influence a modifier, to control particles emission for example ; it may be wanted by user to have a display close to render by minimizing or setting to zero Opacity slider.
So, it could be welcomed as an option that could be disabled ; but probably not as a fixed internal behavior.