Not sure about SAM, but definitely PCIe 4.0 isn't supported on my x370 board, so with that in mind I might be better off waiting until the next round of CPUs/chipsets come out.... although PCIe 3.0 still isn't a bottleneck with even a 4090 as far as I understand (and even only a few % with PCIe 2.0)
That's interesting, if that's the case then I'd be more inclined to just go AM5/Zen4 now, skip the next round of releases and hope a 650/670 board fully supports the features I need on Zen6.
That said though, I do kind of get the impression a lot of the time that MLID just proposes every possible theory of what's coming, then whatever happens can say "I was right"
Of course it could be that, at least in terms of SKUs within a generation, that the manufacturers are just gathering feedback from the rumours to inform their launch strategy, but I don't think that could apply to whole architectures!