I have a poor record of predicting expanion content unless you count the direction the East Coast BoS took from F3 to F4 for which I and many other can say: Called it!
I've seen some people say that they loved the BoS since F3, I've adored them since F1 and been digging them in F2, F3 and utterly loathed them in NV.
With that said there have been many different iterations of the BoS, some more canonical than others,*fake cough Tactics fake cough* and I have no idea where they are going with their ideals and goals in the future but this is what I hope for:
Many have noted that the BoS with their knightly ideals and feudal structure meshes quite well with Arthurian themes and little Artie Maxon now Elder Maxson in F4 do have many things in common with King Arthur, being of a "royal" line, being sent away to foster parents, having a Merlin-like mentor in Elder Lyons, uniting what was once divided and so on, they even call their airship the Prydwen.
Why not build on that concept? Imagine this:
If the BoS are around post endgame then the fate of the Institute and *spoiler character* has some members of the BoS start asking some pointed questions about cherished ideals and the cost of the current policy and an invitation is sent to the other BoS factions, the Mojave and the Midwest BoS for a big gathering to discuss the future and direction of the faction as a whole and to see if there is the possibility of true unification.
The Mojave chapter sends as their representative a cute scribe with a power fist and her bald bodyguard, Veronica and Christine are back! Yay! They are also totally in love. Sweet.
The Midwest chapter sends three representatives, a human Paladin, a ghoul scribe and a super mutant knight.
The East coast/Outcast brings to the table the strength of tradition as well as the strength and dangers of technology.
The Mojave remnants represents the dangers of isolation, xenophobia, unquestioning loyalty and unthinking adherence to tradition and the Codex and bad leadership, such as Father Elijah's moronicity.
The Midwesterners represent the strength of diversity, tolerance and the dangers of having crazy leaders such as General Barnaky.
The questline is then less combat focused and more about diplomacy with expanded dialogue options more like in F3 or NV.
Everyone meets up in a conveniently circfular conference room, maybe even in the Citadel and the end goal determines what direction the BoS will take as a whole.
Depending on your choices in F4 the dialogue and options and responses would be different, Dr Li could pipe up and maybe mention how the Lone Wanderer had some help from ghouls and a totally sweet super mutant(how do we know that the BoS never went against Fawkes? They're still alive!) mentioning how Harkness tried to protect Rivet city even after he was reset, stuff like that.
If the Railroad isn't wiped out then they could point out that the Institute is pretty much destroyed and that the synths could be considered a much lesser threat now that their masters and main production facilities are gone.
If Virgil gets his serum then he could point out that his research could potentially cure other FEV strains thus neutralising supermutants as a power in the Wasteland.
If everything goes well then the Midwesterners reveal a shocking twist! The super mutant is the scribe, the ghoul a paladin and the human a knight, turns out having an extremely tough rad immune scribe can be quite beneficial and useful and prewar ghouls with prewar tech knowledge who are rad immune likewise.
This is just a rough idea and personally I doubt that Beth are even considering anything like this, it is WAY too awesome for their tastes after all.
I just think it would be a great culmination of all that the BoS has been through and in the end the Sole Survivor and Elder Maxson would be the deciding factor, should the BoS continue on the genocidal path they have taken, should they kill all synths, super mutants and ghouls or if they could at least make an exception for nonhostile synths, ghouls and supermutants but still annihilate all the ferals, crazed Frankensteins and rogue synths?
Should they be more or less isolationist, more or less xenophobic, how much should they focus on helping the Wasteland as opposed to gathering tech, is there a good balance between the two?
What do you guys think? What do you want to see? Less talky, more explodey? Deep sea tech retrieval missions? Underwater adventures, ho! More awsome vertibird content?