Only the developers of the derivatives can say, but perhaps the issue here is one of communication.
Was there a clear, and concise, announcement some time in the past about the licensing changes, and precisely what this would mean - down the road - for derivatives?
Or were the devs relying on "forethought"?
If the former, then I suppose the current situation is a consequence of derivative coders not doing what they needed to do - either because they couldn't be bothered, or because they didn't understand what was being said.
If the latter, then it's a case of naivety on the part of Mame Devs.
As it stands: surely the message to people is to download and store any and all front-ends they need for .171, a full set of ROMS, and KEEP IT.
For anything new then you're currently stuck with the embedded UI.
As I have mentioned more than once on these forums, the goals and ambitions of Mame have been pretty clear as far archiving/preserving games. This doesn't seem to have changed.
The issues seem to arise mostly when people want to use Mame to play the games. At that point Mame Dev's seem to not care too much (just my impression, some seem to care more than others, while others don't care at all). This is an odd dichotomy, and a bridge some can't seem to cross.
Add into the mix - and I might as well say it - some Mame Dev's are just plain rude and obnoxious for no good reason. The Internet, sadly, can bring out the worst in people, and it certainly applies with certain devs. Thank goodness we have the likes of R, Belmont who is at least able to have a discussion without throwing a tantrum.
In closing - this isn't good news for the community. Actually it's very BAD news. IMO, Mame devs should at least care about it. If they don't then one wonders why they're involved in the project at all - they might just as well save their work into local storage and leave it there. There's no community without Mame Dev's, but at the same time who are the Mame Dev's preserving things for if the so called "user community" is left behind?
So what happens if someone goes ahead and releases a new version of MAMEUI[insert anything] for say, .172? Mame sues them?