1. Networking support for games that had it 2. Model 2 improvements 3. Sound fixes to Seibu SPI 4. Raiden 2 5. More outputs hooked up for MAMEhooker to exploit (OutRun springs to mind) 6. More gambling games SH4 Dynarec
Not sure there's much else I'm really hoping for with MAME now, it's overall in pretty good shape for my needs.
Well, maybe I could have tacked on CV-1000's re-instatement but I assume it'll return in a few years (so long as SaiDaiOuJou really is the last game on that hardware). Only really missing Daifukkatsu if I'm honest.