I'm pretty much in the same boat - I've been saying I want this for a long time, so I had better get it! I think I'm going to order one and use it side by side with the GRIII for a week or two. I really respect the 28mm focal length, and I think sometimes I can make good images with it. But 40mm I can nearly always get a shot I'm happy with. 28mm is just more demanding.
I might get the GRIIIx and limit myself to shooting with only it for a while, and see what I come up with. At $1k it's definitely not cheap, and something (or things) else will need to go. So I need to be convinced by the lens. It's not going to have amazingly shallow DoF (being a 26.1mm f2.8) and will likely have noticeably broader DoF than the 20/1.7 wide open. But the Ricoh rendering on the 24mp sensor and its 14-bit DNG files are really something.
Ideally I would like this camera to be the best essential everyday carry camera - and I think it will be that. Tiny, fast, normal focal length should give me the ability to compose more easily on the fly without needing to combat the 28mm propensity to distort subjects close to the edges, or having to think as carefully about relationship between near and far elements. The interplay of those is what makes 28mm really important as a focal length, but it can also be a real pain! I honestly think 40mm makes a better snapshot focal length than 28mm. It's a more direct ratio between seeing and capturing what you saw. It's incredibly neutral, more so than a 35mm which is often said to be a neutral, in-between, neither wide nor normal. To me, 35mm is just a bit wide and 40mm is not wide, but wide enough to get the edges in when you want to.
A lot of the talk around this will be as a street camera, and that's probably true. In the covid world, being free to stay a little further back is a good thing. 28mm makes you get close to people if you want to feature them instead of just including them as an element among many in a frame. 40mm is a better people on the street lens. But it will be a tad harder to point and shoot effectively-framed street photos with the 40mm on such a tiny body, at least until I get used to it. Tiny cameras without much grip (the GR is essentially a bar of soap) aren't that easy to point effectively. A little like shooting a subcompact handgun, for those who have, versus a regular frame handgun like police or military would carry. You may have what feels like a firm grip, but the small amount of real estate means there are just fewer contact points and it's harder to get things lined up perfectly.
I am not primarily wanting this as a street camera, however. The GR has never been my main street camera, even though I have used the GRIII fairly extensively on the street. Even though the snap focus is amazing, and I wish every camera had it, and the inability to easily zone focus on M4/3 is one of my biggest frustrations with the format, I prefer to do it the old-fashioned way, on my Voigtlander with the 35/2.5 lens. There's also something about how classic my olive Bessa-T looks with the silver lens, such that, even though the shutter is loud, people just don't seem to feel threatened by it at all.
No, the GR is about seeing the little details of the world and quickly capturing them, and things like the highlight-weighted metering are a big part of that too. I like to get the subtlety of shadows, something that's harder to do on M4/3 with the limited DR but easy with the GR. I really think the 40mm will make it extra easy to compose these sorts of photos. For anyone who's seen Stephen Shore's earlier work with the Rollei 35, it's that sort of photography (maybe fewer dirty toilets than appeared in American Surfaces) that I want to do, and it's what I had the 28mm GRIII to do as well - except that the 28mm lens is more challenging and, while it forced me to take a better, more thoughtful photo much of the time, it also really interrupted the flow state sometimes.
