I am extremely confident a new 23" iMac is coming and will be launched at WWDC. What I am less confident about is whether it will look like the existing iMac (just with a different screen size) or if it will be a new design (and if a new design, will it be more than just slightly thinner bezels?). The 16" MacBook Pro will also get a CPU upgrade to 10th generation Comet Lake.
I am also extremely confident that the 27" will see a spec bump at the BTO level with 10th generation Comet Lake-S CPUs and AMD RDNA 1.0 GPUs. It will also have a new TB3 controller (Titan Ridge) and WiFi 6 and probably Bluetooth 5.0. And I am tentatively hopeful it will have a 1080p webcam. What I am not confident on is whether or not it will look like the current model or it will have a new design/thinner bezels.
Frankly, I don't think bezel size on a desktop display matters all that much to Apple and probably not much to Apple users outside of this forum. And even for those who feel "the bezels are too damn wide", if the 2020 iMac was just the 2019 iMac with thinner bezels but the same CPUs and GPUs, if you had a 2017 (and especially a 2019), I doubt you'd rush out and buy one just for the aesthetics. It would be the new internals that were the driver to upgrade - improved aesthetics would just be a bonus.
October will be when the new iMac Pro is launched along with new RDNA 2.0 cards for the Mac Pro. And if we're lucky, Intel might have their 10th generation "B-Core" out and Apple could also update the Mini while we're at it.
But it does matter, otherwise, why whip up a stunningly sexy looking Pro XDR display with those razor bezels at all? That is super Pro and super expensive, and at a $5000 price tag for pro users only, that is an even tinier fraction of Apple users that would care about that, but Apple still went gung-ho with it.
But anyway, I'm with you on the 23" iMac at WWDC, and at the very least, I expect thinner bezels on it. Not so sure of a full on redesign either, but I'm still hoping for it.