From the password compromise side, not really, you're just pushing the cost of hashing to your users (and it will impact mobile users more). There's a similar t

From the password compromise side, not really, you're just pushing the cost of hashing to your users (and it will impact mobile users more). There's a similar technique on needing proof-of-work on the client to combat DDoS. From the authorization side, there is a threat, because if your table storing hashes is compromised, attackers just have to supply the stored hash to the auth endpoint and they get to login as anyone. A combination of hashing on the client side (or immediately once the pw hits the endpoint) with something cheaper followed by a more intense bcrypt/scrypt afterwards might help a bit with the tradeoffs.