I already thought about this longtime, why do tube amps need that bulky linear psu (but nostalgia) and mostly people who i asked said that it's impossible to make high voltage power supplies that are not noisy (which i tought is bullshit). I even talked with my father (a former aviation electronic engineer) about it and he said it certainly should be possible technically, but you don't t have the right parts in the electronic parts market to do it. In Aviation they already do it since decades, but will militairy spec parts that are not on the general civilian market. The main issue seems to be the the semiconductors (transistors or IC's) for high voltage that are needed.
So it's good it's happening finally now. I like tube amps and their sound, but not their physical weight and heat dispensation. Switching to SMPS will reduce that and give more stabel voltages to the tubes. As long as the filtering is good (is the case since a decade with good ones) the old argument of switching noise should be not valid for this (as tubes are very sensitive to that).