@Donna Fontenot - By the sounds of it, this is only for the admin css, which lives independently of any theme css / less.

If you have a plugin that adds css to the admin, I imagine it will need to be updated for mp6 anyway, but I can't imagine that there will be any conflict, given that SASS/LESS etc are all compiled to css before being used.

Really, for end users and most developers, this change won't affect you at all.

:)