They just announced on facebook that they have now sold out of general entries, but there are still charity places.
12,000. That's a lot of bikes. Fortunately I have a mate who lives in central Cardiff (who I'm riding with) so I'll take my #2 bike to his place some time beforehand, to avoid logistical nightmares. I can either stay with him, if he has room, or stay at a hotel in a neighbouring town and get the train or bus in early in the morning, then leave the bike with him and hop on the train afterwards.
I've never done anything even vaguely like this before, so it will be interesting, if nothing else.