I remember that in a game when I was a kid (Red Alert) it was possible to set the technological level before starting the game, in order to decide if in that specific game session it was possible to develop exclusively infantry, infantry and tanks only, or all (the highest level).

With the same criterion some tournaments of Soldiers Inc could be thought, in which the technological level is set to lev. 1, 2, 3, 4 ... respectively:

- only light infantry,

- light and heavy infantry,

- everything except aviation,

- everything is usable.

In this simple way you could organize PVP tournaments at "technological level 1" where only light infantry can fight.

or "tech level 1" for "Reposories takeover Tournaments", in which only light infantry can attack repositories or extract resources from them.

it could be a good idea to rebalance the forces between the players and let everyone play at the same level (since the rest of the army must be left at home and can not be used!).