It is a good idea, but there are a few options to get it to work.
1. For short term fun, you need to convince a group that is currently playing FFA to go over together.
2. Schedule a set time to play there. (Every Wednesday at 8:00 pm EST for example)
3. Have 3 or 4 players that can seed the TDM server and as much as possible play it.
In all these instances, others guests will probably join, it just takes members working it to make it happen.
Not to put a damper on it, but it has been suggested several times before. Seems most like play FFA and know that they can get a game going anytime they like.
But I'd be all for supporting getting the TDM going!!