So much makes this a terrible idea as a permanent solution, but it could be acceptable as a temporary solution while the migration is ongoing.
Clients will be able to roam. But roaming is always affected. For .1X, there will always be a slow roam between the two worlds, and the clients must go through the entire EAP exchange with the radius server. This is fine for PSK, as the handoff from one AP to the other is always relatively fast.
Regardless of .1X or PSK, the client has less power to choose the next roam candidate as the neighbor reports will not include the APs of the other technology. And you need to ensure that the other world is not classified as rogue APs.
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