Honestly, if this is even vaguely usable, it's going to replace my phone and my tablet, simply by reducing the screen size for both while still having some modern hardware behind it. I find 5" phones to be just slightly too large to comfortably use one-handed (and forget about the larger flagship phones that come out these days). I at least have some faith that I'll be able to reach across the 4.6" screen, although who knows how annoying the large vertical bezels will be.
The tablet side is actually more exciting to me, completely independent of the folding feature. I still don't have a good replacement for a Nexus 7, and this looks like the first tablet that's come out since 2013 that's both close to it in size and on par or better in terms of hardware. The N7 was basically the perfect form factor for my hands, and since I finally gave up on it I've been using an 8.4" tablet that's just narrow enough to hold in one hand but more than uncomfortable enough that I still complain about it years later. Even if the Fold is unusable as a phone, I might spring for one anyway as a pure tablet replacement. If it's also comfortable enough to carry and use as a phone, that's just gravy.
The tablet side is actually more exciting to me, completely independent of the folding feature. I still don't have a good replacement for a Nexus 7, and this looks like the first tablet that's come out since 2013 that's both close to it in size and on par or better in terms of hardware. The N7 was basically the perfect form factor for my hands, and since I finally gave up on it I've been using an 8.4" tablet that's just narrow enough to hold in one hand but more than uncomfortable enough that I still complain about it years later. Even if the Fold is unusable as a phone, I might spring for one anyway as a pure tablet replacement. If it's also comfortable enough to carry and use as a phone, that's just gravy.