Yes you can blend in renpy, and that's mostly whats used, their is actually only 5 animations total in that scene. But i do prefer to do the animations vs blending for a few reasons, actually takes less time for me to do as I don't have to babysit the computer while it works, and phone's HATE blending. Actually had to add a new feature due to this that limits the frame blending because it crashes on a lot of phones.
Maybe I am not fully understanding, All I see is a much slower additive/dissolve transition from what I normally use. I did fade into black allot during that scene, but believe it or not, in renpy, to do that, it has to transition to a black image. My most used transition timing in most cases is 1 second for most the game, but for sequences like that, I transition in 0.06 and 0.04 timing between stills and then 0.1 and 0.5 when fading to black.
On patreon, the voting ended with like 75% loved it and want more of it, the other 25% was more or less its cool, but is it worth the effort. It took about 50 hours to do that scene, so for your average person that's a week of work, but at the rate I work when I am really focused on something, it was 3 days.
and allot of the reason for the really fast timing, is to get as much fluidity as I can. it would be like when you convert stills into a video, you have frame blending, which is essentially really fast transitions to fill in frames so you have more fluid movement and less jerkyness, frame blending just makes things smoother overall. and running fast timing for transitions is essentially doing the same thing, and with a timed sequency, I cant just convert everything to a video because if I need to change 1 thing, every part of the video would have to be redone and retimed. but it has the side effect of phones really hate it, phones don't like to transition between a bunch of images in a very short amount of time.