It's all about the $$$. If you want refs, be prepared to pay. A lot.
A two-ref system basically requires that each team carry a ref. (Two refs per game, two teams per game, one ref each.) Experience with observers tells us that it is incredibly difficult to get observers for games. A couple years ago at Solstice, I arranged to pay the observers $100. I thought $100 seemed like a pretty good incentive and that I'd have no trouble getting observers...no luck. Realistically, you have to push that number up around $300 or more (plus travel) to make it worth peoples' time and you'd still be getting crappy refs. Let's look at the numbers.
A typical tournament is going to require a ref work ~9 hours a day for two days. Even if you call Sunday short, you are still looking at 16 hours for the weekend. You want to pay them $300? That comes out to be $15/hr, which is short of what co-rec referees make to ref city league soccer games. Anyone co-rec players out there think that's the quality of reffing that's going to bring our sport forward? If you want quality refs, you should expect to pay $500 a weekend. Per team. Per tournament. Plus travel. For a Nationals contending college team that's an extra $2500-$3000. For a Nationals contending club team that's an extra $3000-$4000. Nationals not included.
Paying and having refs would not be optional. This past weekend in San Diego, a couple dudes showed up and observed a few Open games, but the majority of the Open games and all the women's games at Prez Day went un-observed. It wasn't a big deal because the current system we have, where the observers follow the players' calls and the players lead the officiation can function smoothly with and without observers. We can play a tournament without observers and it isn't going to greatly effect the game when we do have observers. But refs!? If there are going to be refs at Regionals and Nationals, there damn well better be refs at every major tournament.
At Oregon this year, we have already had two starters leave the team because they can't afford it and a number of the women are scraping by. Adding $2500 in a sport where most teams receive little to no funding or external support would be difficult. It would be difficult for the dedicated teams and impossible for the developing teams. Teams already balk at paying $200 for Sectionals. What would happen if it went to $700? They wouldn't go.