These are what we felt were the CORE mechs and most important to us personally. Some dev's had favorites others are in there intentionally for balance. The other reason the whole group was selected was because of the legs. If you notice we have all three major leg types...and just for clarification the legs are the most challenging part of implementing these guys in the engine. Now we have regular knee, reverse knee and double jointed. It was really important to me to get at very least one of each type in. Because of this once the system has been setup it is relatively fast to implement a similarly constructed mech.
For example. Thor/Summoner and Loki have close to identical legs....so adding a loki onto the list would be fairly easy later on.