I've actually started working on this now. I'm just going to try a regular single player game (although with the ability to create additional save slots).
It's also going to be extremely customizable (which has taken up most of the design phase so far)
When you create a new game, you can choose to customize details - create new /edit existing items, weapons, armor, NPC types, locations (though you'll need to pick an existing map generator, you can add random location triggers like "cell" and "big red button" and "table" and "armory" and have them do a variety of actions based on a skill check + difficulty), and new skills (weapon skills only though).
In addition to it being something a lot of people said they wanted, it will also be nice to have that generic interface for me to change the default setup.
Things that will still be hardcoded include the map generator, skills OTHER than weapon skills, stats, issues, and the actual mechanics.
Creating custom stuff will probably a fairly long laborious process working your way through a bunch of forms, but when you're done you'll be able to save the settings and later share them with the world (or you can take other's pre-built settings and use them). You can also share saved games.
Right now, I'm planning on doing that by creating a "player_slot_generator" flat file for each player save slot that is created and doesn't use the default system to store all those settings, but I'm not sure if that's the best way to do it.
Anyways, once I get up a decent working copy of the generator I'm going to start working on the location exploration bit, and then I'll actually have something to show you guys. But that might take a while - I may not be working my full time job any more, but I AM looking for a new one, and I have other obligations.
(Also, I am planning on making two slight changes. You will be able to load "chemicals" into the syringe to give it interesting effects. This is in many ways a test of the "ammo side effect" feature I intend on implementing to allow things like tasers and flamers without having to make special cases.
Leadership will also be re-implemented, easier to get, and have more of an effect than it did before. It will mostly govern how many people you can effectively bring on missions, and their chance of panicking (which can manifest in a lot of bad ways) or getting separated from the group and having to make their own way home.)