They can’t, I think, but nothing prevents your support contract (and thus access to subsequent updates in any form) from terminating when you release the source

They can’t, I think, but nothing prevents your support contract (and thus access to subsequent updates in any form) from terminating when you release the source. You can do it, IBM will just refuse to do any more business with you from that point on. This kind of GPL not-a-workaround always made me feel a bit queasy, but open access to RH code (even if a bit stale and hard as hell to get to build) alleviated that feeling somewhat. I guess it no longer does.