What's wrong with instant replay? Communication, right?
Mini-mikes don't work. Red flags won't work. What's wrong with simply flashing "review" on the multi-million dollar scoreboard so everyone knows what's going on. That would include the fans, the TV announcers and, of all people, the referee. After review, start a two-minute clock, then flash either "play stands" or "overruled," followed by a brief explanation, e.g. one foot out of bounds, knee down, etc. Ingenious.