First of all i would like to say that Blood Bowl is one ofthe best card game of last few years i played and i played pretty much everything known out there.
My idea came up just a few days ago while we were playing Spartacus Blood and Treachery we really enjoy right now. I really like the theme in Blood Bowl and from the very beginning was thinking about making a deeper and more fun game. First of all i really think that one should consider adding draft mechanic when adding new players to the teams. Like in real NFL weaker teams should get a chance of getting the best player out there at the start of the round. Balance and loosing player keep their chances till the end. With this you'll have to add money or any kind of equivalent to offer while trading so every player could change his strong back breaker for a couple of weak and quick runners for example.
And final thought coming back to Spartacus - intrigue cards played during preseason making your team stronger and other weaker while offering bribes and intimidating. It really can andd much more fun to the game with diplomacy and intrigues not only puting cards on table before you but also interacting with other managers.
Hope somebody from the company would read this and think about making some cool additions in the future.