As some might now since a while, I've always had a slower-pace mod project for unvanquished.
This will be a long term effort, and as such have low chances of success, especially since unvanquished's and tremulous' players seems to be rather fond of fast gameplay, when one does not really tries to survive much but instead tries to suicide dealing as much damages as possible to enemy team. This is fine, but is not the gameplay I aspire to.
This mod will requires a bunch a technical changes, as I want it to be possible to add, remove or modify gameplay elements simply by editing a simple configuration file, which represents lot of work already.
But the idea would be to focus on the actual fights outside of bases, and to besiege bases, which would have strong and expensive buildings, compared to current rather weak and cheap ones. Which means any building with be useful, unlike alien current defenses.
I also want to give a try at a real mining system, with buildings having initial cost, plus an upkeep. Note sure about resource depletion, but it would certainly be nice to have. I'll come up with some idea for that without modifying the maps themselves, ofc. I'm not sure I'll want them to be repairable or regenerable at all, as we can see how it can make games stall in current gameplay and even the experiments.
The fight changes would be based on the idea that there is nothing illimited: aliens would have stamina to manage to prevent their constant hit&run, and humans would have longer reload times, or for no-clip weapons, overheat mechanism so that they'll have to be careful to firing too much in a row.
I have a complete document describing all those ideas and much much more, and I'm not planning to work toward it.
Needless to say, I'll probably integrate AI changes and HUD changes too, but they will not be my primary focus.