I probably still would have chosen Lyons' Brotherhood of Steel. But it would be nice to at least have the choice to do something different.

The Enclave would work similar to the BOS ending. You go into Vault 87 and get the GECK. After you get it, you would be ambushed by multiple BOS Knights and Paladins. You have to fight your way out of Vault 87 with the BOS ambushing you everywhere. You would escape Vault 87 and come back to Raven Rock, telling President Eden about the news. You would fend Project purity from BOS members again, they then use Liberty Prime in a last attempt. LP would be the last boss.

The Outcast would have you earn their trust by giving them technology. After, you can work with them for a plan to overthrow the BOS and then work against the Enclave. You would get the Enclave's help, as they think the Outcasts would just be easy pickings even after they "returned" to the citidel. The Enclave and Outcasts would raid the citidel and they would succeed. The Enclave would then double cross the Outcasts, it would be up to you to save the new Washington chapter of the BOS. You would fight the Enclave Soilders out of DC with the help of the Outcasts. The Enclave would leave the down town area but would still be everywhere outside of the area. In the end, you would find yourself in a final battle with the Enclave at Raven Rock. You would succeed. In this ending, you would not get purity done and instead save the people from the Enclave.

The Family would be the bad faction, it would be only accessible if you chose the cannibal perk. Here, you would work with them in settlement raids. After 5 you would be noticed by the BOS and Enclave. Automatically being made an enemy. After a bit,, you would find a BOS corpse with a journal about water and the processing plant. This would make the Family to try and get it operational for their own devious needs. You would find a GECK in vault 87 and get ambushed by the Enclave AND BOS. They would find you as a serious threat, so they would form a "truce" until you would never see the light of day again. This would fail as you would escape from the Vault after the Enclave and BOS turned on eachother, this would be because they didn't trust eachother to keep you in captivity. After you escape the Family would be waiting for you in the operations room where you would activate the purifier.

This should have been in the game would have improved the game and replayability by a decent amount.

I ultimately hit enclave, but I would NEVER choose Eden. Ideally you would be able to help Autumn facilitate his coup, for the same reasons I chose the ending I did in the (excellent) FO4 America Rising 2 mod.