I'm curious (I hope you can give us a "little spoiler" ! )... are you making three different MAME4all(s) or a single release which supports three different ROMsets (37b16, 0.66 and 0.84) ?
Yes, one release.
There will be a single frontend, which lets you select which version of MAME you want to use, initially the three versions you mentioned will be available.
New versions of MAME will be easily added if desired, perhaps some even later versions.
The new frontend has screen shot and favorites support as well as being able to filter games.
I'm just adding IPU hardware scaling support which certainly helps for games that have different resolutions to the GCW-Zero's native 320x240.
My current favorite is "xexex" - an awesome shooter by Konami!
It's a great game for testing as it really pushes the hardware as it has unusual video mode and resolution but it's a great game!
On top of that I'm making versions for Pandora and Raspberry Pi - so pretty busy.
The Pandora version is looking pretty awesome as well so far as it has very capable hardware.