This is exactly what I proposed before! (read below)
After my post jendrzych the designer of the new icons mentioned that he created a mock-up with the same idea.
Then William Reynish, Blender’s UI designer joined the convo with this:
“Only issue with that, is that then addons need to always supply an icon if they want to add their own category. Technically I would think it should be simple enough”
I’d consider this absolutely OK - especially with jendrzych’s idea that the first two letters of addon’s name could be there if no icon was provided.
But the discussion died at this point - I haven’t heard about this since then but I really-really hope they get back to this idea after 2.8
It’d make so much more sense (especially if they implement my drag and drop idea with it) and would be so much more professional as you said.