Well, I hope we can see a difference in the quality of an image in a 90MP sensor compared to the 45MP sensor. I hope we can, but I will have to see it to believe it. If the IQ can show enough improvement then I'm very interested in it. Let's hope that they can make other big (or tiny) improvements over the R5 so that there will additional reasons to get it over the R5.
Regarding pixel shift, am I the only one who doesn't give a **** about it? IMHO it will be worthless for handheld photos or photos with any subject motion (which is most normal cases). If you use a tripod for a shot of the Grand Canyon then the rocks aren't going to move so you might have a chance of more resolution than the 90MP can give, but even then I'll have to see it to believe it. While I would be happy if it really could happen and it'd be great, I view it as almost entirely a marketing gimmick which camera makers feel they have to highlight or else they'll lose sales.
Speaking of new high end R bodies, I wonder if they're going to offer a R5a (astro) version, where the red has more sensitivity to H-Alpha? That would be interesting, even in a 45MP sensor.