That date might not be as late as you'd think. For any paid exits to be included in Chelsea's financial accounts for 2022/23 they must take place before June 30. This is almost a requirement for them to pass FFP and why Mount is leaving so quickly.
Yes, I agree. I don't think that there will be any "official swap" deal in the works but lets say that Chelsea are keen on a Brighton player (for this example and all of our feelings for Moises, we'll use Sanchez), it would make a lot of sense for both clubs accounts to pay a premium for those...