I can't see KEF offering an upgrade for existing R users, but it would be cool if they did. As an owner of R5's for a couple of years now, there's no chance I'd upgrade to the new Meta versions, as there simply won't be a big delta between them because there wasn't really a huge delta to the Ref's (diminishing returns and all).
The current R series already sound excellent and so for me it's either save up for Ref Meta, or, wait until the 3rd or even 4th generation R series is out and perhaps then consider changing. Speakers aren't iPhones and don't need changing every year!
However if KEF were to offer an upgrade option, then that's actually about the only feasible way they have of extracting more money from me. For a reasonable fee I'd be inclined to do that upgrade.
I've got LS50 Meta in another room, the current R's already have a sweeter treble, so it's not like MAT is transformative by any stretch.