How quickly are replays shown to fans on calls by ESPN or FSSW? It takes like 10-15 seconds to produce a high quality, slow motion replay and it's usually pretty obvious what the "correct" call should have been.
The idea is that the refs on the floor should not be waiting for the special refs to make a decision on every call. The special refs need to make these decisions swiftly using normal "downtime." If the special refs can't keep up, then the game should not be slowed down.
Even if the special refs are only able to review and give input on 1/4 of missed calls during a game, that's still an improvement.