If it took 11 years to get to 75%, that means WoW will be 100% in 3-4 more years, or roughly 2026, plus or minus a bit. Even assuming that GRRM is one of those rare writers who requires very little editing or polishing (meaning, his "manuscript" is close to a final draft), we'd still need to add in another year or so for final polish and publication, so likely looking at 2027 at the earliest. If he can't pick up the pace for book 8, as others have said, it is likely a pipe dream.
Anyhow, the main problem with reshooting seasons 6-8 is that it isn't only WoW they need to do it properly, but the eighth book as well. But let's be optimistic. Let's say that GRRM picks up the pace for WoW and finishes it in two years, not 3-4. So it is done sometime in the second half of 2024, and published in 2025. Then let's say ADoS goes much quicker, more similar to his previous books, and is published five years later, in 2030. So the series is complete in 2030...11 years after the end of GoT. Now you're dealing with another problem: the actors are all 11 years older, some may have passed on, and frankly, the demand simply might not be there to revisit GoT. I mean, by then we'll have seen HotD finished, and probably several other GoT series start and even complete...including a sequel series with Jon Snow that may develop and/or answer some dangling threads left by GoT.
I would also argue that the show itself was pretty good through season 7, that the main problem is season 8 and how quickly it resolved not only a major plot of the entire season--the rise of the dead, and vanquished in just one episode!--but now we learn from HotD, a prophecy hundreds of years old. In other words, HotD made the end of GoT even worse.
I think the best way to rectify that would be to...well, bring the dead back in the Jon Snow series. Meaning, the Night King was just the precursor of a greater rise - not truly a king, but a herald. He was just "softening them" a bit for the true Long Night. This isn't a perfect answer, and of course would require a whole new story for HBO to potentially botch without proper oversight from GRRM, but is at least worth considering.