Maybe the even cooler thing to do -- and something that would really utilize a computer based platform rather than just paper cards -- is to have heroes along the lines people are discussing, but they actually gain experience points by being played in winning games. For example, if I play my Time Hero and win the game, that hero gets 1 experience point. Experience points can be banked and spent on increasing power & toughness, decreasing casting cost or activation for effects, maybe even buying new effects. This way, each Time Hero would be slightly different from other Time Heroes played by other players.
It might be complicated, but I think it could be kind of awesome...