I was thinking, in order to make the journey immersive (and since the route of DC-to-Vegas is somewhat questionable in terms of rail), that a somewhat more complex quest line could be integrated in order to begin the TTW. What I had in mind is that, for the first time going West, the Lone Wanderer has to encounter three intermediate locations and fix their problems before he can continue his or her journey. Once these locations are cleared and the final journey to the Mojave is complete, these locations (except one, obviously) can be revisited at any time later. Perhaps they could receive further development seeing the consequences of the courier's actions in the intervening years. I'll outline what I have in mind. Ideally each of these locations have at least a half hour's worth of gameplay, meaning the resolutions to continue the journey are relatively simple but still involve some fetching/fighting.
Prelude - The Lone Wanderer hears from a traveler from the West about a city in the west where fortunes are made and shelter is found unlike anywhere in the Capital Wasteland. The traveler, who has never actually been to New Vegas himself, passes along stories of individuals walking into casinos with only a few caps and quickly becoming wealthier than Mr. Tenpenny could even dream of (the traveler cites him as he knows the Wanderer will have heard of him). The traveler gives the Lone Wanderer a pre-war tourism brochure (which the traveler assumes to be fact, a high intelligence Lone Wanderer can express skepticism) and marks Union Station on the map.
#1 - The Slide - The Lone Wanderer arrives (two days after his departure) via rail in the ruins of pre-war Slidell, LA, the end of the line. He finds a sizable militaristic village there. The bridge to New Orelans is out, and the residents inform the LW that that New Orleans itself is heavily ghoulified and Slide fends off monthly ghoul waves, and that one is coming soon. The ghouls seem to be growing stronger, and the leaders of the populace say they will help you continue on westward if you help them get the best of the ghouls (this will involve repair skill, fetching defensive assets). Alternatively, the Lone Wanderer discovers the hordes are controlled by a cabal of several non-feral ghouls who seem to have been pre-war business magnates. They can also promise the LW safe passage if he/she chooses to sabotage Slide's defenses. The Slide will climax with a major battle between the residents and the ghouls no matter which side the LW chooses, and on any subsequent visit the courier will encounter an increasingly militant but growing power in the Slide (following a victory over Ghouls that lead to their weakening) or a population of ghouls, many feral (but non-hostile to Courier) inhabiting the town. The Slide world could be easily built of assets from Point Lookout, as the Louisiana-swamp setting is in full display.
#2 - Hastings - The Courier has heard that rail travel functions west of Hastings, Nebraska, and follows a path involving a Mississippi river ferry and overland travel, arriving in Hastings a month after departing the Slide. Hastings itself is mostly empty save for a few wasters and caravans who have happened to settle in the town. However, the Lone Wanderer finds that the city has two rival Vaults on either side of the city find themselves in a state of constant hostility (the rival vaults being part, of course, of the vault experiment) and often attempt to raid eachother. The caravaners inform you that the train and rail broke down some time ago and that those in the West are unwilling to risk the Legion (which the caravaners hint at but don't fully understand) to come repair it, and that those in the Vaults are the only ones who could likely repair it and the rails. Either Vault is willing to help if the Lone Wanderer helps them gain the upper hand on the other (they have alternative plans; one Vault seeks to drill beneath the earth to enter the other and bypass their door, while the other vault wants you to gain their trust and betray the opposing vault). Alternatively, the Lone Wanderer can get the two Vaults to agree to peace. Hastings itself could perhaps use generic urban assets alongside some Freeside assets. Upon returning, the Courier will find a somewhat xenophobic dictatorship over the town if he/she chose one Vault over the other (the vault dwellers will populate the town itself plus their vault, while the other vault is sealed from the outside), or if the Courier chose peace, the town itself will be heavily populated with both new wasters but also residents from both Vaults. The Courier will be able to play Caravan for the first time in Hastings. Before leaving Hastings, one of the caravaners who helps fix the train alongside the Vault-dwellers will make you promise to deliver something for him in California.
#3 - The Divide - Following another two weeks of travel, the Lone Wanderer arrives in the Divide, a small windswept community. You deliver the package you promised to, and are told that you are the first Courier to arrive in the location for as long as anyone could remember. Here, your choices are not as open as the other two (since Lonesome Road's canon locks the Courier in). You'll be tasked with several things to help the settlement grow, and you'll have to do these and the residents will guide you to your destination as soon as they are complete. You can do several more Courier quests in the Divide, and many tell you that this is a profitable career choice in the West. You hear that the claims about New Vegas's wealth-making capabilities are overstated, and you can decide that instead of going there, you'll do Courier work mainly in California, though either way you state you'll be back through the Divide. Basically this is more immersion and lore-friendly solution to TTW travel than any kind of particular new travel thing, but it lays the basis for the Lone Wanderer becoming a professional courier and beginning work in the Divide, eventually continuing to work both as a courier and continue building up the Divide until the events described in Lonesome Road occurs. This can obviously be done using Lonesome Road locations minus the crack in the land, and some also generic Capital Wasteland resources in the windswept Divide climate.
Here's the kind of map I had in mind:
http://i.imgur.com/KGv3ztm.png
It's a bit much to ask but I figure it would add a lot to the experience of the mod. I have no mod skills whatsoever but if someone actually wanted to do this I could lend my voice.
.
, I am sure other team members will take a look as well and we will see what happens in the future 
.
