BK ATC Management used to apply its own limit: 8 in the training circuit at any one time. If you've ever flown with 7 others in the training circuit - especially at night, and even more especially if there was a mix of types - you'd have to agree that 8 was a big number. Led to a few stressed pilots and controllers - especially when you add a stream of high performance bank-runners arriving.
Personally, I think 6 in the training circuit is a reasonable limit. For arrivals and departures, I think it will only be a problem if both circuits have been combined with one ADC - then it'll be 6 in total (+ 1 discretionary departure). (That, of course, will be every night.)
They do need to get on with writing a published procedure if you're at an IRP and either can't get a word in on frequency or the TWR won't let you into the zone because of too many already in the air. The last midair at BK was at an IRP, and orbiting at TWRN or PSP is a recipe for disaster.