There were plans for a supposed 2.5 at one point a couple years ago. Then if I remember correctly when other new sources came along with 4k80 on the horizon, it was decided just to skip 2.5 all together and just go the way to 3.0 which has no eta . Only being told it’ll take a couple years.
He said on YouTube with the release of the new 4K HDR on Disney+ he’d be redoing a lot so it’ll probably take quite some time. Like you said, I’d imagine it will be measured in years. For now we can just enjoy what we have!