The inability to log in with the existing account adds a cost to me.
I don't have too many steam friends.
Adding as a non-steam game seems to be the only practical thing to do, but what does that really accomplish over just keeping AH as a steam-independent game.
So seems the easiest, best thing for me to do is simply nothing and trust that AH will get the benefits of Steam exposure without existing uses like me trying to actively promote it.