Well I took that as read if there wasn't scope for 2 full departures in an hour there wouldn't be scope for more! Also, edit noted!
It does raise the question of whether you could get the business at Ebbsfleet or Ashford to fill the trains in the peak. 1tp2h to each destination is probably fine for the off-peak, trains are busy but you can usually still book quite late before departure. It would only be 1 station max either way, but you'd need to take about 500 passengers across that period to take the pressure off St Pancras. It's borderline but not impossible. The big question is whether you can staff the intermediate station (almost certainly Ebbsfleet) efficiently enough to avoid taking a loss on the operation.
The fact Eurostar aren't looking at it suggests they don't think they can.