You wouldn't even need direction antennas to do this, just some number of reasonably spaced omni's that could feed signal strength information. The problem with this approach is that the wrist band needs to transmit to make this at all useful which adds cost to its design vs being a simple receiver only.
I mentioned this in another comment but it should be easy to correlate a seating assignment to a wrist band MAC giving you reasonably good location information. It wouldn't work "in the pit" obviously but you would be very hard pressed to get any accurate enough location data in an area like that.
What if these bands are paired to phone via bluetooth so that the base station can send commands to the phone (through the mobile network) which in turn relays it to the band - would it allow a more fine grained control with acceptable latency?
Latency would be huge with that setup. 900mhz radio has more than enough range and bandwidth to handle 50,000 - 60,000 devices updating several times a second. I've used LSR [0] modules in the past for prototyping and they have a gateway that would allow you to control the entire thing through ethernet so any computer could run the program and just spit out ethernet packets to send control information.
I mentioned this in another comment but it should be easy to correlate a seating assignment to a wrist band MAC giving you reasonably good location information. It wouldn't work "in the pit" obviously but you would be very hard pressed to get any accurate enough location data in an area like that.