I don't understand why you continue to limit your thinking to top players.
Here's one name - Moise Kean. We want to sell him before the window closes so we can reinvest elsewhere. There's interest from the continent, and we need a deal to be done with enough time for us to do whatever we need to do to replace him. There's less pressure on the buying side if the European window closes a week or 2 after ours.
We'd also likely sell in that scenario if the offer was right for FFP / squad mood reasons, even without being able to replace him - which would not be optimal.
Don't really think it would cause much issue for us. We just would have to do our business earlier and make it clear we sell before a certain date or he stays. It would force us to be much more proactive and that is a very good thing. We are very slow, disorganised and reactive and the later window will just encourage that even more. I only see positives of the window closing before week 1.