That’s a really good question and I’ve been thinking of starting a similar thread, because I pretty much come up empty when I think about this.
The only thing I would have added would be related to community growth and attracting new users/contributors. Most highly active users here have really old accounts, like 5-10 years. I don’t know what happens to the ones that seem to vanish forever (abducted by aliens or whatever) but it’s a little concerning as old timers seem to “retire” and we don’t get a whole lot of new users to fill in the gaps. This is one reason I’ve put the site back into my regular daily routine to help where I can.
More on the topic, I do agree with the comments above regarding shadows. But I’ve always figured it’s hard to do in a way that looks good in every case.
A mesh manipulation library would be nice too. That’s something I’d have found great use for in the past (and possibly future). But this is hardly something turning people away from using the engine.
Better JavaFX integration maybe, but that’s external to JME. (I don’t think we really have a great solution for keyboard event management yet.)