I'm not guessing any more, as I have friends that work at the various motherboard makers here in Taiwan. It's not BS, it is what it is right now. Why would I make this up? Not for the fame, that's for sure. But hey, you don't know me, so that's ok. Let's just say that I've written for a fair few publications over the years and I live and work in the tech industry in Taiwan, so I might have some inside information at times... Also, there's nothing scientific about this, technical maybe...
If you'd read my post, you would've seen that they haven't decided yet, due to the fact that they haven't seen the final boards and made sure they pass the stringent requirements for PCIe 4.0. This is why they decided against it on X470, as those board designs couldn't meet the spec. So if all the board makers have done a good job with their B550 boards, it'll most likely have PCIe 4.0 support. If not, then I guess we'll see.
Oh if you knew how often I've heard this, not only with IT, but with (german) car brands aswell. It's always someone who knows someone working in the industry. But they can never state names because of secrecy etc.
I just can't imagine that it works this way, AMD waiting for the OEMs to try to pass the requirements and then deciding on a feature, like: "Oh, nice try everyone, thank you for your efforts, but that's not enough, we can't risk that, so pless sell your near-Gen4-supporting-and-thus-costly-boards only with Gen3 and for a lower price.
That may have been the case with older AM4-boards were Gen4 wasn't planned and they weren't even sure if they could fit Zen2 onto the plattform (on TR4 they decided against it). But on a new Chipset, AMD has to plan beforehand what features it is going to have.
Only two explanations I can imagine. One, PCIe4.0 for the chipset was planned but proofed to costly to reliably work, so AMD decided against it later on an forbids OEMs to support it on B550, like with the older boards. But then B550 would bring to little benefit over X470 to justifiy such a long wait.
Two, PCIe4.0 was planned only for when Intel would bring it on S1200 and will be disabled when Intel really doesn't support it because of problems, like recent (wobly) rumours suggest. Like when AMD waited with the 5600XT, if Nvidia would decrease the price of 2060. But that, too, would mean OEMs had to develop costly Gen4-supporting Boards, even successfully in this scenario, only to not use it.
I stay with my previous opinion, B550 itself will probably only support Gen3, while the Boards will support Gen4 on CPU-Lanes. Only reason against the latter would be if it would make the boards to costly because of electric requirements.
A choice that may make people buy Ryzen 3000-series not only over Intel alternatives, but also over heavily discounted Zen+ CPUs.
