Here is a very old suggestion: The friendly play https://netvor.sk/trac/arcomage/ticket/31
This would allow players to play test games, so the game outcome would not effect the score.
When challenging, a player would choose option "Friendly play" and the when accepting, the other player would be informed about it in the challenge message.
This feature would motive players to test more strategies, without the need to worry for their score.