My oppinion is that, more than wanting to pile up more features to Neverball, I think the most important is to create the conditions to have people create more level sets, otherwise it will all evolve around Mehdi and rlk's levels. (Of course, I like their levels very much, but once you play them 100 times, they get a little boring).
For this, I am creating a level set of my own, for which I have some levels created already, which of course . The problem I am facing is the lack of good documentation (specially for someone who doesn't want to create or play quake levels). Please note I am *not* blaming anyone for this, specially rlk, I can only thank him for the great job he did creating this game in his spare time. However, the current mapping documentation is directed to someone with a broad experience with gtkradiant and the common problems that arise from level creation.
So, I think a better documentation for level creation is a vital issue for neverball's success, and if someone considers forking the game, it will still need docs.
If someone with idle webspace on their hands, that would manage to set up a collaborative documentation effort (like a wiki or similar), to improve the current mapping documentation, I'd be willing to help.
PS: NeverBowling? Funny, I have a level called NeverBowl, which mimics the bowling game. 
