A tricky plot, but if used correctly it will guarantee that you win multiple challenges during the round. Jon Snow can participate on offense, despite the restrictions here. Margaery Tyrell and all of the strength boosting effects can also guarantee you have more strength at your disposal than your opponent.
Unfortunately, the best decks don't really have any trouble winning challenges, so this plot will likely fall short of being generally good. Maybe if very defensive decks become a tournament staple.