Will lemming tribes be implemented? You know, custom skins that mixes with the regular Lemming groups in gameplay? Also, will the project support all L2 skills and Lix skills at some point when the project goes open source?
No. Custom skins are possible, but only as a "all lemmings for this level" thing, not mixed within one level, and there are no plans to change that.
Likewise, not all skills will be supported. Some Lix skills primarily exist due to their usefulness in multiplayer, the Batter being the biggest example here - those would have little reason to replicate in NL. Others, we already have a very similar skill, even if it's not exactly the same, for example the Stoner as the NL counterpart to Lix's Cuber.
In L2, many of the skills are duplicates or near-duplicates of each other. NL has no reason to replicate such a setup. Some of the skills that don't fall under this are purely execution-focused, such as fan-based skills and Superlemming, and those kind of skills do not fit with NL's design principles. Even ignoring those points, there's simply too many of them.
The project already is (and I believe always has been) open source.
Not quite always; but it's been open source for a
very long time now.
There could feature ideas that nobody thought would come into being and there they are being added to a version update.
Reaching a final version isn't about implementing, or even considering, every idea anyone can possibly think of. It's about deciding at some point "this is enough, this is going to be NL's final list of features, and no more additions will happen'.
Of course, as it's open-source, someone else could take over, either under the NeoLemmix name (if the community chooses to accept their new versions) or a fork under a new name, similar to how NeoLemmix itself forked from Lemmix.
Jumper is the only skill that's been given any serious consideration, and in the absence of some really significant unforeseen issue with implementing it and/or it turning out to not be very useful in practice, that one is going to go ahead. Some other ideas have been floated around, but most have been rejected; and all of those that haven't (except, again, the Jumper) are on the "this can be given further consideration but I'm not outright convinced yet" pile.
If anything, I think it would be time to do another feature poll, what would you like to see before features stopped being added?
It's not just about what features people would like to be added, it's also about what features - both in terms of individual features, and in terms of overall quantity (or rather, time spent) - that I'm willing to keep working on NL for. Though also, again - see point 3 in the original post too.