We are already using .NET 6.0 on Linux. If you install Microsoft’s .NET 6.0 package on Windows, you can get the “new” performance there today, though to be fair the gap between older versions of .NET and 6.0 is much smaller on Windows.
In our project planning, after Mac is released, we’ll move iOS to .NET 6.0 then Android. Android is the most difficult of the three, iOS should be straightforward. At that point everything will be unified across all platforms, and we should be keeping in sync with the best performance Microsoft has to offer going forwards.