Saying this from the perspective of an aggressive NVfag in the midst of his 800th playthrough and hates Bethesda:
Emil Fagliarulo says New Vegas is canon (and also just outright canonizes Tactics?):

(
link) (
archive in case this nigger backtracks)
He states there's a 15 year window between New Vegas and the show. 15 years is a pretty feasible timespan for shit to go full retard, especially in a shithole like the Fallout setting. NCR turning bandit in that time is over the top, but not impossible - a stable government only lasts as long as its most competent heads. Rwanda went from almost normal to full nig incredibly fast once the Belgians left.
Additionally, there's no date slated on that timeline chalkboard for the nuking, and it isn't just where "the fall of Shady Sands" is. It could mean NCR as a whole just falling apart, which New Vegas was outright warning was on the precipice of happening as it was spread too thin, its economy too beaten up, and the attempt to claim Hoover Dam being too expensive from all fronts. I could see it falling apart in damn near every ending, even the NCR one depending on how it goes. Plus there were numerous indicators that the Mojave was relatively fucked regardless of what you do even without Lonesome Road or Dead Money's local issues being stated to be moving towards the Mojave.
The final shot also shows a (slightly) less dilapidated Mojave before showing off the New Vegas ruins, meaning if this piece of shit somehow gets a second season, they'll have opportunity to explain what the fuck they're peddling.
This doesn't justify shit like completely 180ing Robert House's character or the Enclave still existing or
cold fusion being achieved, but I'm pretty sure this isn't an attempt to completely decanonize New Vegas, just an attempt to snuff out having to focus on any minutiae from the game.
And the show is shit anyways and I can still play New Vegas, so I ultimately don't care that much.