Borrowing somewhat from last year. Most of these are totally unrealistic, but WTH:
* Votrax SC-01 sound chip emulation for games like Q*bert and Wizard of Wor, but also the few Apple II Mockingboard games that used it.
* Qsound emulation
* Support for cross-platform rumble/force feedback effects (assuming it's even possible via SDL 2.0 etc)
* Continued psx driver improvements (really nice stuff from smf and others this year)
* DC driver speedups, assuming any more juice can be squeezed out of it
* SNES SuperFX improvements
* Tighter coupling of MAME and MESS
* Someone finding Bouncer and Stern's Journey (the latter being a machine featured in some Starcade episodes, really amazing game that might have been a classic but for its rarity, even at the time. Probably no longer in existence, alas)
* More schematics found for discrete circuitry games to complement Couriersud's amazing work