He's talking about the Cave hardware.
It worked in v143u9, but support was pulled for v144 after Cave contacted the MAME team and asked them to remove it.
Apparently, they are still selling these games, so it was in violation of MAME dev's own policies anyway.
Personally, I'd drop the issue.
If everyone posts tutorials and releases alternative builds just to run these games,
it will only serve to damage MAMEdev's reputation and set up for legal obstacles for future developement.
I have a lot of newer games running on my setups using other emulators,
but this is MAME.
MAME is different. It's focus is on preservation.
These games aren't in any danger of being lost forever if they are still being manufactured.
It would be a shame for the whole project to go down the legal toilet over a few shmups.
If someone were to build a standalone emulator for this hardware that doesn't use any MAME code, I have no problem with that.
If they get in trouble, not as much is lost.