Legion has no future, Caesar's Legion is an epitome of "le working well on paper" as there is no sign of a functional leadership to takeover when he dies, which by the look of things will happen either soon, or sooner. One of his big plot points, if I remember correctly, is looking for a suitable heir. The way his Legion enforces military discipline through corporal punishment and random acts of violence is comically ineffective. Further more, has Legion shown any signs of being able to commit to grand acts of architecture and infrastructure, beyond merely securing the roads from raiders? The actual material conditions that made Rome step up from it's neighbors. The brunt of Legion's forces, the tip of the spear that will roll back the NCR and ensure a new Rome can't even fix a single howitzer, something that the player can do, given the right parts, without any required technical expertise. Whether he wants it or not Ceaser is a LARPer par excellence, though something he is not aware himself.
Mr. House boasts often about his capability for organization and production, as the only real force to bolster productive forces in the post-war America, but so far his actual accomplishments have been far from impressive. Thanks to his own legion of pre-war robots, he managed to jump start electricity production (thanks to a lucky geographical and infrastructural position first and foremost) and restart Vegas. But what is the real accomplishment of Vegas? Bringing some tribes to heel thanks to superior firepower (and given incidents with Omerta family and White Gloves, not even that good), making them play out pre-war fantasies and fixations (something the Kings done without much outside influence) and most importantly bringing back the scale of gambling unimaginable before into the post-apocalypse. For all his technocratic boasting, his most impressive practical achievement has been hooking up wastelander scavengers and junkers to slot machines and sitting them down to poker tables. Beyond the sheer income force of this economic model, New Vegas is hardly a self sustainable model, given that most food production seems to be handled by the NCR. Much like Vegas itself, it's all glitter and glamour made to impress the player with promises of the far, far future, the actual scale of achievements is far from jaw dropping.
Meanwhile, Westside is a much more humble, and often overlooked part of the game. A small, relatively thriving community (thanks to Followers of the Apocalypse) with a self sustaining food production, internal security force and a limited, but decent trade economy, despite sitting on the edges of Fiend's territory, one of the most brutal, aggressive and erratic of the wasteland's raiders. Westside's success, if the game offers it in one single word is "co-ops", as in farming co-ops that help the community stand on it's own as a self sufficient model. Though not particularly powerful or influential, they are certainly lot more stable then Freeside or New Vegas Square communities. If there is any "message" supplanted by the in-game information, it's that any hope of the future lies in the model of the Followers of the Apocalypse and their efforts to reach out communities, tribes and cultures such as Westside. Even Great Khans, raiders that they are, are a better potential force for the wastelands future then either Caesar, Mr. House or NCR's bourgeois apparatus. It's not about replenishing civilization, it's about taking the material conditions of the wasteland and building a society that suites them, a society that can therefore extract required resources to build it's own productive forces.
I could be wrong on all accounts, this is only from my memory and there could be material outside of the game that completely lays waste to my room temperature takes.