Here some ideas I had in the last weeks. I will not make any of them myself, but I thought why not tell them here, maybe someone is interested.
1. TFTD or XCOM community mod collection
Basically only bugfixes and slight improvemets (like fixing the lightning/ avenger doors and ramps, someone made this already), a collection of single mods which can be activated one by one instead of a mega-mod, in the style of the Openxcom default mod.
2. A Xcom 2012 to Xcom 1995 conversion, making it as close as possible to that remake.
3. A LONG WAR version of the same.
4. XCom 1950-1970. Enough such mods have been proposed already, so I will not go into it any further
5. A mod that fits between (time-wise) between XCOM and TFTD.
6. A Zombie-War mod, where you fight zombies and other corporations/blocks.
7. A Russian Xcom mod, there are AK-47 and Mig-31 icons outhtere as well as RPG and many others....
I will MAYBE try to update two of my tiny equipment mods for TFTD (the Tranquilizer and the Breaching Charge), but that is all I can provide in the future apart from feedback, minor resources and ideas.