Hmm I thought I replied to this. From what I've read, Infection will be featured in a private game lobby only. So the lobby leader has full control of the settings they are given. I think with CoD:Elite players will have the ability to vote for which playlist they want featured in public lobbies.
I have created a couple custom games, one being infected. You can read a description of them here http://www.callofduty.com/message/106115599#106115599 They are available in my vault and hopefully I can get them in the community playlist. Both games are fun with about five or more players.