UEFA will still need the stadium for most of Sunday for media and removal of branding. Then the EFL branding would need to be set up It wouldn't work. The same thing happened when United played Barcelona in 2011. They kept one final on the Monday, and moved the others to Old Trafford on the Saturday and Sunday because they needed the stadium for those two days.
Monday is out of the question for the Championship Playoff Final as UEFA require all players to be released from their clubs by the Monday for the Euros.
The government, Sky, EFL and UEFA will all find agreement and the Champions League final will be hosted at Wembley on Saturday 29th March because:
- EFL need to keep the Governement on side for next season's return to stadium
- EFL and sky will be compensated financially
- UEFA will have more fans at the flag ship event
- UK Government avoids any travel complexities for fans and players returning, and has prestige of hosting event in UK
The only potential sticking point is if the UK Government are going to be hard on the number for fans, but I doubt this will be the case.
The Championship Playoff Final will almost certainly be played at the same time slot, at a different venue.