When they are talking about accelerating the merge talk, it does not mean days or weeks. I would say it still in terms of months. That's just the talk. Once the terms are agreed upon and the merge process started, they would still need to get approval from a few governments (mainly US, EU, and China). That would take at least a year or two.
So we'll probably hear the decision in the second half of this year, and maybe the merge done mid 2024 or early 2025.
As far as HDD-SSD split, it would probably easier to merge first, figure out where the overlaps, and get rid of them. If we split first, then we'll probably need to hire non-engineering functions such as marketing/sales, HR etc. because we are forming two companies. And then if merge happens after that, they'll potentially have overlaps.
My guess is they would merge, and send all the Flash BU engineering to Kioxia. Just a guess.