Okay, this is a thing introduced by Fallout 3 and it is criticised by many. At first I thought it was a little bit of a stretch, the Enclave hauling ass across the country can make sense, since it's established that they have a base in Chicago and they apparently had more vertibirds up their sleeves, but the BoS doing the same seemed rather strange. However, I found http://www.falloutwiki.com/images/0/0b/Coast_To_Coast_Map.jpg map which seems to show a clear cut way to the East. Most of those settlements don't ring a bell, I'm guessing they're VB or Tactics material so I don't know much about them. So I have a few questions.
1. When exactly did Lyons start his expedition?
2. Did CL exist by then? If so how strong were they?
3. Were they at war with the NCR already? When exactly did the NCR-BoS war start?
4. Is it plausible for them to go along that path of civilization? How hostile are those areas?
5. Because of Lyons' disobedience the mainline BoS stopped supporting him at some point, but officially they still said that they are a part of the organization. How do you think they sent support when they were still sneding him? I'm guessing only small parties could go. Also when did they cease support? (Arthur Maxson was sent because his father was killed outside Shady Sands. At that time he was still bros with the other elders meaning that it was sometime after that that they stopped)

The Enclave don't have a base in Chicago. They have an Outpost(s), there is a difference and they most likely set it up on their way from Navarro to DC. They weren't an army just remnants.

The Midwestern Brotherhood are very different from the Orginal Brotherhood. The two groups will not work together. If they did I am sure Lyons would have mentioned it. Part of Lyons mission was to find them. I believe his way to DC took him around their territory.

1. Lyons was in DC for 23 years. So around a year before that maybe is when they left. Or thye got to DC in the same year.

2. Not sure if CL existed, if they did they were just getting started. The wiki says 2247, so yeah they did exist but just starting out. Where wiki got that date I have no idea.

3. We don't know. Sometime after Fallout 2, so 2241-42.

4. Plausible for who? The BoS, NCR or Caesar's Legion? either way I think it isn't.

5. Sometime after they sent Arthur Maxson. I am guessing small groups as well.

Also Lyons Group isn't an army. We know know the most likely reason for the BoS sending him was because they needed tech for their fight against NCR. A desperate act. And since Mr.House is connected to Optimus Prime, the BoS back west must have found some info on it, Hoping it was still in DC sent Lyons.

I would think the BoS/NCR war started about a decade after FO2, maybe later.

If you look at Van Buren for clues, I think that has a lot of details on war, however, what will be official from that is questionable.

I'm fairly certain in VB both the BoS and NCR attacked Navarro together. Personally, I think that should continue to be the case, because imo, just the NCR doing this raises skepticism for me. Not because i don't think that eventually they could have done it, but you are talking a lot of casualties. Then, you talking a lot more casualties in BoS war, any minor battles we don't know about like against raiders and such, then of course war with BoS in Mojave and Legion.

That is a lot of warring. How the NCR could accomplish all this non-stop fighting kinda boggles me.

I don't think Lyons was sent after the BoS/NCR war started. Otherwise there would have been a greater sense of urgency to return, and not just stay in the CW going on 3 decades.

Speaking of which, isn't there a line in NV about rangers "chasing ghosts"? I almost wonder if that is a reference to an elite BoS unit that uses stealth boys and in VB forms their own faction? It could be.

CL would have been weak, and assuming travel through central/northern midwest, where MWBoS had been, I don't think it would have been too dangerous.