I see you use Gimp. Just in case you’re not aware of it, there’s a nice supplement to Gimp (perhaps even an alternative, in many cases) out there that you might want to check out: http://krita.org/
And to add to my own first post, one huge thing I forgot to think of in terms of suggestion for improvement is better support for other applications besides Maya. I’m surprised how much Epic Games cater to Maya (even more than Max, even more surprisingly), all while catering UE4 towards an indie development market. Many indie devs don’t use Maya/Maya LT.
Some of us use modo, Cinema 4D, Softimage (may you live long, Softimage 2015!!!) and Blender. Also, it wouldn’t be a bad idea at all to perhaps team up with Marmoset to just load up Toolbag scene files (.tbscene) natively.
I know Maya (and Max) have the best .FBX support, but as long as FBX support continues to improve elsewhere (I know you’re aiding Blender’s FBX support, for instance), and Autodesk FBX Converter is freely available, I think other applications are worth supporting.
Also, folks, don’t forget to check out Unreal Engine’s road map page on Trello. I only say this because I see some of your suggestions are already in consideration there, some as highly-voted. Though, I guess it’s good to remind them again. 