I don't hate them but the games I consider canon have made it clear that they are a faction in decline because of their own failing ideology and politics.
Bethesda ignored all of that when they made Fallout 3 because they wanted to make the BOS the "cool" Power Armor wearing faction.
Frankly, I don't think that's the direction the Brotherhood is moving in. Its their arc from FO2 to FNV, sure. But I think we're going elsewhere with them.
I think the future of the Brotherhood is to disperse into multiple different groups. Think about it:
1. We know from the Fallout New Vegas Official Guide (and honestly, good sense) that the Core Region is pretty much picked out when it comes to scavenging things and tech. The one big exception we know is Big Mt, which is somewhere in California - its where the Kingston Peak used to be, if I remember right.
2. I think its logical to affirm that the Brotherhood has large popullation growth. For one, they have very good living conditions in general. Proper nutrition, exercise, pre-war tier healthcare, cybernetics. Also, we know from Veronica that the Brotherhood is big on natalism and general "making babies", because its their only source of growth. Which is why the Brotherhood is not big on homosexual relationships.
3. It makes sense that the Brotherhood sends out expeditions outside the Core Region. Big population growth and not much to do in the Core Region. It is simply logical to send expeditions to obtain more technology elsewhere. We know they sent expeditions to the Mojave, Montana and D.C. The NCR has destroyed quite a few brotherhood bunkers so I suspect there's more Brotherhood scattered around that we haven't seen - say, other parts of Nevada, maybe Northern Cali, Oregon, etc.
4. The assembled body of knights of a military or
knightly order was also referred as a "chapter”. The Brotherhood has been using the term for a while now. You know where else a similar term exists? Why, in Warhammer 40K, used for the Adeptus Astartes chapters. We all know Fallout has a lot of WH40K DNA, nothing wrong with that. But the Chapters only came to the fore after the Horus Heresy, they used to be big legions.
5. In WH40k, the "vanilla chapter/legion" was always the Ultramarines. They're the "generics", but deeper down, they are also the all-arounders, the versalite chapter that's able to adapt. The later foundings and other chapters from different legions are the different ones with weird flavour. Which is why people often say the Ultras are "boring", but that's not true. They have their place. If everyone is weird, no one is weird.
6. What's my point here? Well, my point here is that Lost Hills = Ultramarines. The old school Brotherhood is the default template to apply on. Lyons' boys would't be different if the Lost Hills guys were just like them, same for Arthur Maxson's boys and the Chicago Boys. Its worth noting that both Lost Hills and Macragge changed with time and their founder's absence. Both forgot or sacralized their histories.
7. Bethesda is revealing in F76 that the Brotherhood didn't use to be as isolationist as they became. He was open to outsiders and did all of it for their sake, it was his son and the others who were isolationists. Which gells with High Elder John Maxson saying that their last outsider recruit happened two decades before the Vault Dweller got in. Also, worth noting that the Brotherhood doesn't care much about the softer sciences, like history and psychology.
So what's their future? I think their future is for the organization to disperse in general. Lost Hills will never archive primacy within the larger organization ever again. The Brotherhood will have many chapters spread through the wasteland, and each chapter will become its own thing, with its own specialties and quirks and their own doctrines. There will be classic techno-religious isolationists, feudal-fascistic conquerors who openly recruit outsiders, charitable knights that dislike mutants and synths, insane tecno-dictators, a chapter that is defacto part of another state (like the NCR), etc.
So yeah, I think Bethesda is playing an interesting game here. They can have their cake and eat it, too. There will be Brotherhoods of all flavours now. Is the Brotherhood declining? Yes. Also, no. Of course, the question is if they can implement it right.
