A GMS2 style graphic editor would be great
I don't think a new editor would be a must have since there are very powerful and affordable graphics software on the market. However I'd be interested in some improvements there regarding animation preview, etc..
That mail made me feel like it's Christmas again! I can't wait to read more news about C3. The new logo looks great, it's modern and minimalistic (and I hope it refers to the colours of the new interface).