rankings and matchmaking came to mind
There are a lot of plans in place for that already.
Elo is actually a fairly weak rating system for a game like this, because it's based purely on win/loss. If you have a lot of other data -- like kill/death ratio, flag captures or returns, and various other metrics, you can have a system that's much more responsive than Elo. (We home-rolled an algorithm for DCL that seems to get people pretty close to right within usually 2-5 matches.)
how to revitalize the D1/D2 community. It seemed to me that if playing D1/D2 was as easy as clicking next, next, next, "Find Match" then people would start showing up
The D1/D2 community was like 5 people 3 years ago. It's been slowly revitalized -- Rangers brought some people back, and then Jediluke and kiln brought some people back, and Retro/DCL brought people back, and the Steam release brought people back, and D:U brought people back. I think we've had about 80 people active in multi, which is not huge, but it's a big gain over a couple years ago.
Making it even easier would probably bring a few more people back, but I think the main thing is getting the info out there. We occasionally lose someone who doesn't want to install/configure Descent, but more often we lose people because they either start playing and lose too much, or they don't realize that the game is still around.
Still, something tied to D:U that lets people launch D1, D2, or D3 would be super nice. We've got about 11,000 people who have paid money for D:U right now, and we'll probably get more like 100,000 when the game hits commercial release. Even if only 1% of people who pick up D:U are interested in the other Descents, that would drastically increase our player base.