I think, maybe they show us what is possible with the new engine, cause the engines used for B1942 and BF2 (almost the same engine, just some extra unlocks and new graphical engine) cannot really have walking animations for vehicles 
But it is possible they gonna use this kind of mechs in the new game, I think C & C also has this kind of mechs and C & C is made by EA ( in the past by Westwood) and DICE is part of EA, so I think it is pretty clear in what direction they go (Commander in BF2, u played the commander in C & C)