I imagine that those are to come sooner or later.

An idea for these could be not crusaders but vehicles or big units that take 3-4-5 slots of different forms that you can use as basement for different current crusader to team and boost their abilities.

Say, a tank where you can put 3-4 attackers and boost their attacks
or a Pirate ship where you could sail 4 gold finders and boost the gold thing, etc...

Those vehicles could be also leveled and improved with cards.

salute!