I would very much like to see Game play tokens in shop. These could be traded and sold for game gold. Since monthly is basically 5 dollars and 500 Sovereigns cost 5 dollars you could make them 600 Sovereigns and make a little profit for making them available. Also you could make 3 month, 6 month and 1 year tokens as well.
My concern here would be it's a vector to convert RMT into gold which isn't great. I'm already not a fan of anything from the sovereign shop being tradeable as I'd prefer to keep any semblance of P2W out of the game.
100% would support sov purchases being bound. It would be ideal if you could redeem the code on any character linked to the web account, but once the code is claimed, the item is then bound to that character or account.