It is what it is :-P I actually just thought of a great use for it as I'm sitting here typing this.

Maybe some kind of ban list, where before either player starts choosing their team, they have a chance to ban their opponent from playing certain cards.

They actually added this in brawls 2.0 - there is now a Guild ability that allows players to ban 1 card from each opponent, in home games.

There could be modes where you each get the chance to add modifiers before the battle starts.

I really like the sound of this! I really like the idea of running custom battles (like you described or even setting the mana/rules) as well. At least for friendly challenge matches, if not for tournaments. If I want to run an whole tournament that is no magic, no legends - why shouldn't I be able to?

As to the difficulty due to lack of interaction, I can definitely see that - I guess they have already covered a LOT of the basics. I can think of a handful of abilities :-)