Supposed seating chart for Wembley
The stadium seats 90k for football in just the seats alone, based on this they have a little less than 2/3rds of the normal seating capacity open. Figure the seats themselves are around 50-55k and then the A-G seating around the ring probably takes it to 60k or so.
That would be a hell of a gate on its own. They could always add seats if tickets move quickly.
Will be interesting to see what happens when the sale starts.