Remains to be seen what exactly BE will be offered to move to CWL or Cardiff City Centre, but as you say MathersWales it will probably be £££ with incentives from the WG due to being in the Enterprise Zone.
Roger Lewis said that BA has thrived at CWL, so there would be no reason why BE wouldn't (his theory not mine). Just a bit of a logistical nightmare, and of course whether BE would accept.
With it would probably be more based aircraft at CWL i imagine.