DLC works on large games, such as the Call of Duty series or Halo series, It is easy because they run off many servers.
With HTC, it would be extremely hard to implement at server with the DLC and have enough people to populate it.
Say 200 people download the nuke for the B29, they would have to be put in a different server, an then only those 200 people could use the DLC together (max of 50 people in arena at one time).
DLC is just not going to work with a game with this small of a community base, now if we could get another 100,000 people, then your talkin!