> It's the end of the line for many of the thousands of users of derivative builds, > certainly.
MAMEUI has already completed its relicensing effort - it consisted of needing to contact 3 people, 2 of whom are semi-active posters here. MAMEUI and MAMEHB are going nowhere; they'll be out for 0.172 right on schedule. GroovyMAME and MEWUI have stopped, but that's because all of their features are part of MAME itself so those users can come home.
Moreover, MAME's license is now compatible with the largest library of code on the Internet. It is easier than ever to make derivative builds now that MAME is under a license everyone in the community intuitively understands.