BA CityFlyer has hired a lot of self sponsored students from FTE over the years as well as sending quite a few mentored students through, (as did BA Connect before it was broken down into BA CityFlyer or sold off to FlyBe).
Certainly with the last few courses I don't think they had a set number of places in mind, but it usually ended up as either two or four at a time. The most recent 6, (four or five years ago now) were from separate applications and went into two separate courses.
This is the first time they've gone for the MPL so things might be different. But I'd guess it'll be around four places again. Any more would be quite a risk for a small airline, and I suspect FTE would want that as a minimum to make it worth their while, It'll almost certainly have to be multiples of two for the sim.