well... I did not know that.
It makes sense for artists to use Flash editor, and it looks like Autodesk Scaleform is it's own implementation of Flash Renderer (supporting 10.1 and AS2/3), so as long as it supports OpenGL then portability shouldn't really be a problem. I would have thought most AAA game UIs where made in Max/Maya/etc, but It's true many 2D effects are easier to create with masks and gradient tools (plus you have ActionScript). Still.. there's nothing stopping anyone from making a great UI in Blender on Linux for future games :-) and it doesn't look like Scaleform would/should be a big reason not to port major games to Linux (as far as I can tell)... depending on how fancy Scaleform's getting with it's ActionScript VM...
Looks like I should have done a bit more research before posting. Autodesk Scaleform already supports Linux right now, check out the integration page (http://gameware.autodesk.com/scaleform/integrations).
Which is great. It means this shouldn't be a reason CS:GO wouldn't be ported. Very exciting, I'm really hoping CS:GO does get ported, it and Skyrim are my favorite games.