Two possible alternatives to arrow keys - alt and ctrl modifying, and multi-step selection. No idea how they'd work in practice, but they sound cool in theory.
I know not all keyboards have the same layout, I'm basing this off a standard QWERTY keyboard with regular ctrl and alt keys. This could be modified to work with other layouts, I think.
Here's alt and ctrl modifying:
1-8: Select card from hand
If the card targets only creatures (i.e. adrenaline):
* alt+w - alt+o = creature in opponent's top row
* alt+s - alt+k = creature in opponent's middle row
* alt+z - alt+< = creature in opponent's bottom row
If the card also targets players (i.e. lightning):
* alt+\ = opponent
If the card targets permanents (i.e. explosion):
* alt+q - alt+o = opponent's perm in top row (u, i, and o are shield, weapon, and mark)
* alt+a - alt+k = opponent's perm in bottom row
In all cases, swap alt for ctrl when targeting yourself.
Other possibilities:
Esc: Menu
Settings: P