There's a "substantial equivalence" clause in the deeming regulations which I believe blenders will use to get around having to go through all this nonsense. After all pipe tobacco blends are just different variations of the same thing.
I may be reading it incorrectly, but it looks like the applications & the reports would have a deadline, so after that, you would still have to deem anything new.
Presuming applying for & getting SE is a lot less expensive than deeming a new blend, it seems like the easiest thing to do if you need to put out a new blend now, would be to take a grandfathered or deemed blend, re-badge it, maybe change the cut if allowed (I couldn't figure that out), & apply for SE on the re-badged already deemed/grandfathered blend.