Didn't they announce years ago that it was being developed for next gen systems? I was definitely under the impression that there was never a PS4 or Xbox One version planned...
The first announcement for it was in 2008... back then, PS4 and Xbox One
were next-gen systems.
However, who knows what that project has in relation to the game they've actually revealed as BG&E2. That teaser had Jade and Pey'j as its central characters, and by the time the game was re-announced, new characters were the focus. (I'm not sure if Jade is even in the sequel? Supposedly there's a young-Pey'j being teased and this is a prequel project, although I'm unclear on the story known so far if anybody can help.)
There was also "target render" footage leaked (which Ubisoft weirdly game out officially later?) of a BG&E2 level, with what looks like Jade in an open, encounter-filled chase sequence.
You are correct that, when the 2017 re-announcement came of BG&2, there was an idea that it was a heavy project and was maybe pushing into the next-generation of hardware. AFAIK, they never even announced any platforms for the project, so them saying PS4/X1 is canceled may be the first confirmation they were ever trying to fit on PS4/X1 in the first place.