[martinald]

Yes, but you also have loads of Eurotunnel (car and truck carrying trains) and Southeastern High Speed (non-international) trains on those tracks.

Add the capacity of those in.

Say 3x Eurostar, 5x southeastern hsr and 4x eurotunnel.

The new e320 trains have 900 passenger capacity (could be more with less first class, so let's call it 1000). With 12x departures per hour that's 12,000, and there would be more spare capacity left over because there wouldn't be local and express trains mixed together which kills capacity.

I think you could easily do 15k p/h on Eurostar + related infrastructure. Maybe more if you used TGV Duplex double decker trains.