Pretty much this. Some genuine Pepega takes in this thread. Blizzard could have been working on this since BFA, since Shadowlands start, who knows?.
Not to say that the timeframe proposed doesn't warrant some genuine skepticism, given the patterns of announcement-release we have had for other expansions in the past, I would much rather be optimistic that the team have learnt from the errors of the past, and I guess the proof will be in the pudding come beta release time if this is a rush job or how far the team are actually along (and where I will personally reserve my judgements for)