it's all politics. It's all very complicated and I'm sure I don't understand it all, but before the last America's cup Emirate Team New Zealand made an agreement (possibly with Luna Rossa, maybe with the financial backers) regardless they made an agreement that the next cup would be a mono hull no matter what if they won. Next, they all said during the races that the way Oracle handled it was terrible, that the boats were too expensive and unsafe and that there were too many rules changes, arbitrary ones. That there should be a level playing field with an economical boat so the average yatcher could participate instead of conglomerates. Finally in order to make the entire thing a success they needed to have the boats race at a fast enough pace so they could get the desperately needed tv revenue. If they went back to the monohulls of the 50's nobody would watch. Too slow.
So what we are left with is a completely impossible design. The long fragile arms will need battery and electric engine assist, the boat will be unstable at all times (in the current design) it will be much slower than the catamarans. The entire reason behind the mono hull to start with is to please the traditionalists. Most yatchers are traditionalists. Very fussy about their boats, they despise the foils and monohulls and believe themselves to be some sort of captain of a clipper racing the tea routes of the 1890's. So the main backers of all of this hate the new boats, the new cats, that's where the "must return to monohulls" thing comes from.
It's a complete disaster of a design. The specs are all vaporware, it's not fulfilling any of it's conditions, cheap? no, traditional sailboat design? no, fast? can't be as fast as a catamaran ever.
This is what happens when politics infests a sport, but it's the America's Cup. Politics like this goes waaaay back. All the way back to the original cup when America first captured it, they added this little line to the race rules "All boats must sail under own power to the race site" and the Americans because they were hosting could always build their boats lighter and the challengers had to build their boats slower and more sturdy for crossing the Atlantic Ocean. You ever wonder how the USA could retain America's Cup for nearly 100 years, well that's why. then there all the challenges of the 70's the lawsuits of the 80's and now this.
that's what America's Cup is. A bitter sordid, political struggle where nobody plays fair and also the most amazing and wonderful sailing race in the world. Can't wait to see what happens next. I suspect lots and lots of lawyers everyone sues everyone if history is any guide.