I'd guess the separations used would be the same as for the current procedural approaches - assuming a non-radar enviroment, then you're clearing traffic for an approach from a particular fix or beacon. Where I used to work there were a couple of different IFR procedural approaches for each runway, but essentially we would clear traffic to leave the minimum holding level to fly the approach, and descend subsequent inbounds to 1000' above the go-around altitude until the first one had landed. At that point the next one is cleared for the procedure, and so on. As you're keeping vertical separation it effectively doesn't matter what track the aircraft takes once it has left the fix, as you can't see it anyway! Procedurally you can't really expedite traffic, at least in the UK.