Yeah... so can you tell me WHERE in game that you got your information that the WCBOS is not talking to them? To me, it makes no sense to "cut them off" and not talk to them at all... yet keep them within the organization? I'd imagine they'd want to hear about oh... say the Enclave; or perhaps be updated on anything new they learn about the Super Mutants; etc. etc.. No where in game does it ever state the WCBOS stopped/refuses too communicate to Lyons, just that they weren't going too reinforce them anymore.
Your idea that just because Casdin isn't an essential character somehow excludes him from anything... is your personal opinion, nothing more. Bethesda sets certain characters as being "essential" when they are either a companion, or extremely important to the main story line or a major side story in the game. Casdin wasn't, though to be honest, I think they really missed out on making an interesting side story with the PC being able to either reunite the two broken factions back into one, or 'siding' with one against the other.
Oh, and in a lot of peoples last game, they nuked the Citadel and wiped out the Brotherhood. What you and other people did in your games is not lore, not until Bethesda announces what they consider the lore to be. FYI, I'm not stating something is lore, I'm speculating to the possibilities that could happen.
Actually, it doesn't, it just states that locals are making up the bulk of initiates. Nor do we know how big Lyons BOS was prior too the schism and after it. As for the Lyons Pride, so what if they have 3 of the 4 known and named Knight Captains, that has NOTHING to do with what we're talking about.
You should study history some, personal loyalty does not always transfer down from father to child, for instance Toyotomi Hideyoshi ousted the son of Oda Nobunaga from power and took over. Also, Lyons BOS had taken huge losses after Optim... I mean Liberty Prime. And to be honest, just because they know the Super Mutants are low on FEV doesn't really mean their war with the Super Mutants is going to end any time soon, or if they'll come out in a favorable position after. Lyons "dynasty" hasn't been proven anything, and would've lost without the Lone Wonderer saving them... that's if the LW didn't blast the Citadel too pieces.
And again, from my perspective, while they respect Owyn Lyons as a leader, I always felt like it was more due to the West Coast Elders still recognizing him as the Chapter's Elder.
Because if Owyn's dies, and the WC elders want him as the new chapter elder, how many of the original BOS members will refuse? This is speculation, but it's based on the BOS codex, if the Council of Elders puts forth Casdin as the next chapter elder, I'm not sure many original BOS members would actually object to it.
As far as we know, that comment can only be taken as referring too the Capital Wastelands BOS chapter. And no, we don't know if contact with the West Coast has been cut off, please reference an in-game comment/quote from FO3 that mentions that Lyons BOS has lost communications from the WC; or that the WC is refusing to talk too Lyons.
We know that they are angry over them leaving, we don't know if they've actually broke out fighting. We also know that many of them sympathize with the Outcasts too... And considering that Bethesda hasn't laid down what is cannon from Fallout 3 yet, the Lone Wanderer could've destroyed the Citadel for all we know. Though I don't doubt that they'll choose the Adams Air Force Base/Enclave Mobile Base being destroyed, it isn't confirmed until Bethesda says.
Okay... the Council of Elders lead the BOS into a war with the NCR. A war, mind you, that for every one well trained member of the Brotherhood, there was about 1,000 NCR soldiers. I really don't think they'd have a problem with trying to put someone who would be friendly to their cause, as Lyons replacement, regardless of whether they believe they have authority to do so or not. Also, no, it's not a hard thing to sell, because Casdin left to continue the original orders, which was to find, obtain and bring back tech from the Capital Wasteland too the West Coast. They'd view Lyons as the traitor... but chances are they haven't removed/stricken Lyons from the Codex because he's on the other side of the country, and because he has Arthur Maxson under his care.
This is the weakest point of your argument. Bethesda designates certain characters "essential" because they are vital too the main storyline or important quests. So your argument that Casdin isn't essential somehow makes him less likely to be used later on if they DO bring back the CWBOS, is moot. After all, you can kill Owyn Lyons if you choose the Citadel as the target at the end of Broken Steel... which I'm sure half the players who played FO3 seriously wanted to do from the start.
As I said, it's speculation based on what I think COULD happen, and I've already stated this chance is extremely small. But if they DO bring back the CWBOS for FO4, they should be giving us closure on what happened with the Brotherhood/Outcast schism.