The AMC/Universal spat: First, I think this will get resolved in some manner, and, while AMC and Regal appear committed to it, they will likely use it as a hard stance to renegotiate terms with Universal to show their movies.
Second, this could also hurt Universal. Trolls World Tour could have just been the perfect storm situation for the $20 rental to work - an established franchise, early stages of the quarantine, etc. It's also not even clear how "successful" it really was for Universal. The figures have ranged from $70+ million to $100 million. That apparently is still not break-even for that movie yet.
Bill Simmons had producer Jason Blum on his podcast a few weeks ago, who runs the production company Blumhouse Productions - whose movie The Hunt also was doing the straight to VOD model because of this. He was talking about one of the things they would be looking to see with this model is how much they lose from the regular rental stream that normally exists. Normally, you have the theater revenue. Then when it's first released for rental you have another wave of income from people renting it, along with people purchasing, prior to it then going to a streaming service, etc. There are thoughts that doing it this way could be combining those into one and they may lose a good portion of that regular rental revenue, so they're not sure the viability of this model in all instances.