Like an earlier post mentioned, this actually isn't the first time this has happened, kind of. Remember way back when the Doctor had his hand cut off and poured his regeneration energy into it and it sprouted another Doctor for that Rose? Also if you want to keep the Timeless Child idea *ducks all the tomatoes* this could be how said species reproduces.
Last thought on the idea though, I do like the idea that the Valeyard and the Curator both could be previous splits. And if we want to keep the idea that there were Doctors before Doctor #1 like the Fugitive Doctor, the Valeyard could have split from one of those, and be the cause of the "myth" of bi-generation in the first place. On the other hand, the Valeyard was supposedly at the end of his regenerations, so maybe splitting means the "infinite" regens only follows one branch, and the other has the usual limited regens?
I did like that they called back to some of the major previous events, like the Key to Time, and especially Logopolis considering someone just brought it up a page or two back in comparison to the Flux.
There was one other "blink and you'll miss it" comment that because they're time Lords, they're doing rehab out of order, which while on the one hand seems to be a way to let the new incarnation run around without having to angst about the Flux, but on the other hand makes me wonder if bigeneration eventually reverts....
Okay I know I said I was done with talking about the bi-generation but that jsut struck a thought in me. The fourth Doctor had a forced regeneration by merging with "the Watcher" because he otherwise wouldn't have made it. At the time, they said the Watcher was the Doctor all along, then later when they reappeared for the 5th -> 6th regeneration, they said they were unregenerated projections of the next incarnation. Could the Watchers instead be previous bi-generation splits, that they attributed to projections because it was just thought to be a myth by that point? And that was how the 4th-> 5th one worked, by the bigeneration re-merging to help make the transition?