For the next MAMEUIFX release there will be support for MR MRS PACMAN (hack by Dave Widel) and 1942C64 (hack by Minwah). I'm not sure about the 1942 Free-Play version. Aside the ability to have attract mode with free play, I don't see any relevant change in it. No offence to anyone involved, it's simply my opinion. For this kind of things I believe there's already HBMAME.
no offence taken, the free play was more created for REAL hardware , in fact it was made on request of James (RGP) for Arcade Club so his machine doesn't develop screen burn as his place is FREE PLAY, you just pay entry fee.
I just thought adding it to MAME would have been a good idea as well for the few people that use MAME to run individual games or where some that like to run a game for a week and rotate each week with a different game on mame.
only problem is as you say there is no real "HACK" "CHANGE" in the game itself, but that opinion is not held by MAME DEVS and they wont add it to MAME for being as they would see it. a "HACK"