Dont think that has happened in awhile for MAME. But yeah the emu community has its share of people like that. Grouchy guys who if you do not play by their rules they just ban you. There are other emu guys that are great to work with. There are also some reformed grouchy guys. But you can still tick them off. I think the guys who are holding onto the old hw are starting to realize that the stuff just is not worth much and yes that stuff is rotting. It was just not designed to last 40+ years. There was a point in the early 2000s where it seemed like every other week someone was mad someone else had dumped/emulated something that made someone else mad. Not so much anymore.
MAME itself has some of this too despite basically being a GPL2/BSD codebase.
There are a lot of rare things that are completely unavailable only in the hands of a sole collector (usually Japanese). Then they'll mail it around to friends under a strict "no dumping rule". They like showing off what they have.
Now of course those "no dumping" rules have been violated over the years and usually to disastrous effect but also you have situations where the rom dump is ALSO only in the hands of a few people.
Like what? I honestly don't see why these collectors have enough leverage to impose any disastrous consequences. The rare stuff is in most cases merely a curiosity. In the long run it doesn't really matter if those things are preserved. It would be nice but it certainly doesn't justify bending over backwards for a collector and their "rules". Devkits for example would be extremely important items but I don't see people talking about stuff like that very often.
When Labyrinthe/Horror Tour 3 leaked, the collector went absolutely apeshit and stopped giving anyone access to anything. And that was a ROM collector downstream of the collector with exclusive physical copies. It was someone who wasn't supposed to have those dumps and probably burned a lot of (if not all of) their connections. https://kotaku.com/collection-of-rare-japanese-games-leaks-o...
Keep in mind that a lot of the rare stuff ends up helping contribute to emulator development/accuracy.
The importance of devkits (and these are still hotly collected) only goes so far as decapping ICs is hard work. A finished game might show you new valid opcodes or undocumented system call you weren't aware of.
Keep in mind that the way collecting works in Japan is more about archiving and a rare few people get things into their collection because they are trusted. They're trusted to preserve it, but also entrusted not to make it available to everyone who wants to download it for free. Creators revisit prior works (or make available for resale) far more frequently than we tend to here.
Don’t forget the incredible amount of work that goes into releasing an even halfway decent emulator. Just for pirates to run with it sending thousands of useless bug reports your way.
I thought non-commercial licenses were an old tradition in the emulator community. Snes9x and MAME code were licensed as such for a long time. I've seen developers release code under GPL/MIT/BSD and then object to how other people using their code. Is this what you mean?
In the end, none of these licenses matter anyway. I seriously doubt anyone in this community will ever sue somebody over license violations. People do nothing while corporations file DMCA claims against screenshots despite Sony vs. Connectix.
MAME had one of those style licenses. They switched to GPL/BSD because of your second point. It did not really matter as the companies making these knock off devices/packs had zero intention of following the law anyway, and the people making the emu did not have the money to go after the offenders. It was also a pain if they really wanted to have someone make one of those devices with your code. For example if one of the orig rightsholders to the roms wanted to use MAME they basically couldn't because of that license. For a large company it does matter for import/export and risk management.
People releasing code GPL/MIT/MIT and then getting mad when someone they do not like using it is always going to happen. Not everyone agrees on everything. In the emu case it was more they just did not want to get sued.
What I think is more interesting is there are still devices being created that are using the older code before the switchover that has the restriction and the emulation is worse!
Also Before that Sony v. Connectix it was not very clear, with takedown notices every few months to the sites. Now you pretty much only see the notices on the rom sites. By the point the case was done the license was already mostly in place. Even switching over to the new one was a large undertaking that they put off for a long time. I think a small handful of drivers they could not find the orig authors to ask and they pulled them out and re-wrote them.
MAME itself has some of this too despite basically being a GPL2/BSD codebase.