I understand the sentiment, as I felt that way about Julio Cesar. But I'd say we're so short that it should have basically no impact on the attempt to find a permanent body. We need at least two; getting one on loan while we're looking for ideal candidates is just covering ourselves.
They're not going to stop looking or not sign someone else if O'Brien comes on loan. It's worth nothing that cap doesn't really have to be affected if Nottingham Forest plays ball, as they'd have to pay him either way, so might not be looking for a big salary pickup.
And by MLS standards, he's a really good player.