Remember match-mode selection, Add a "strict-format" deck-size meta-match checkbox
1) Please have the Arena client remember the prior match-mode selection across sessions.
Most players play a single mode (Standard, Brawl, Alchemy, Historic, etc.) most of the time. It's annoying to constantly switch away from Alchemy if that's not one's preferred match style.
2) Please enable a "strict on-format" deck size checkbox. If I'm playing best of 3 in Standard constructed, I'm not going to waste my time against a 200+ card deck that's not remotely competitive. These grossly off-format decks wouldn't be accepted for entry in competitive play at the vast majority of local LGSes or FNMs and they, likewise should be able to be excluded from competitive Arena.