What is concerning to me is the enabler of Flash, and definitley a strong card in Oath, Storm and GAT and that is MScroll .
In my opinion, Merchant Scroll shouldn't be restricted or what ever. It's not like Flash is the only deck that can take advantage of this amazing card. Probably something like half the decks in vintage use it. Gush isn't restricted, so I don't see why Merchant Scroll would be. My logic is probably really flawed, but meh. 