I only had a short play so far, but I found that 2.8 makes both editing inside Rhino and Bella GUI a lot better. Being able to assign Bella Materials in Rhino helps a lot. And in GUI finally seeing Layer names and Object names instead of a bunch of database IDs makes scenes a lot more manageable – finally I know what item is what, without having to reassign materials, check IPR what element changes and then renaming :o).
I ran into the same RH 7 Material Editor quirks as tdegremont reported (it happens all of the time, regardless whether the window is docked or floating). I could not make the image placement from Imgur work, so here’s a link to a screengrab. And in Bella GUI the Rhino Mouse Mapping (nice addition!) the Zoom direction is inverted.