Basically, I suggest that there be a turn limit for every game, say, 60. If after 60 turns no one has won, a tie is forced. Neither player wins. No one gains or loses score. No one gains wins or losses.
This would prevent those situations where both players have an endless Eternity loop, while also allowing for future anti-deckout cards to be introduced.
Nothing too major, but I feel it would be good for the game; things shouldn't be able to go on indefinitely (see: quanta cap, HP cap).