As I doubt anyone on here, or in the press, will have actually seen his contract, I would guess its all speculation.
However there was talk when Launchbury & Daly re-signed that they were promised that "Wasps would be continuing to sign world class players" That, like any potential Training ground clause, sounds vague enough that a decent lawyer could argue it hadn't been fulfilled, or had, depending on what their client wanted. '
At the end of the day, if a player wants to leave, whether his contract is up or not, its pretty pointless to try and keep them. They won't be giving 100% on the pitch, may be a morale problem in the team & could be wasting a decent wage which could be better used elsewhere.
If a player really wants to go, then unless you want a massive squabble, you're better off sucking it up and moving on.