Single player improvements would be nice, but there's really not much demand for it. Consider that there aren't very many people who actually release single player stuff (I'm talking about things that actually get finished, not projects that are started and left incomplete), and most of the people who are working on things will want their work to be accessible to as many people as possible. For me that means vanilla jj2, 1.23 or 1.24. No special hacks required to play it.

I'm sure a lot of other people who make levels think the same way. A good single player project takes at least a few months to make from start to finish unless you're some kind of machine, and you don't want to put in that kind of time investment when only a couple hundred people will even be able to play it.

Because of this I don't think it's really worth blur's time to put in a bunch of single player specific features in JJ2+ which will only be used a tiny amount, even though I have to admit I'd like to see just what could be done. Better to focus on multiplayer, where virtually everyone can benefit from it immediately.

In my opinion, if there's ever going to be a jj2 hack or patch that expands the single player game, it's going to have to actually come from someone working on a single player project.