You loose 8 lanes Gen4 just for the connection of the chipsets. Plus it makes no sense to connect more than one SSD
You loose or you invest lanes for expanded connectivity. Glass is both half empty and half full, depending on perception and point of view.
Chipset silicon is much cheaper this way, and all additional lanes on the second chipset make a difference between B650 and X670. It's really simple - either less connectivity or more connectivity.
If anyone wants even more, which is rarely the case, there are boards maximizing the connectivity and x4 AICs with USB4, SATA, NVMe, etc. Research also shows that the usage of secondary x8 GPU slot is low. And Gigabyte got rid off it. You can love then ir hate them for that, but it's a clear signal for their buyers - if you use only one x16 slot for GPU, here are boards for you. Asrock and Asus more often than not have two x16 slots, running at x8 idmf both are occupied, for those who need more connectivity.
It's about choice And there's plenty of it.
The IGP's probably RDNA 3.5 based on the rumors for Strix Halo, just guesstimating so don't quote me on that. Like I said for someone using it for their work (i.e. printing money) it could make sense if their work is (extremely) time sensitive. For XPU/NPU it was used for copilot(?) IIRC as well as camera & maybe background noise(isolation) as well. Definitely for cam so it would be helpful in similar tasks.
Yes. Ryzen 9000 will have a substantial update on iGPU, with at least RDNA 3 engine, probably 2CUs, plus we expect XDNA cores on the silicon too, in readiness for Windows 12 Copilot and other tasks.
iGPU update is another improvement on I/O die, so I don't understand when people say "it's the same I/O". Well, clearly it's not.
The only thing AMD could have provided better was integrated USB4 on die rather than discrete solution via ASM4242. They have had integrated USB4 since Rembrandt APU, it has finally arrived on desktop APUs too with Phoenix, so it's time that 'regular' desktop CPUs also integrate USB4. Arrow Lake S will have TB4 integrated, the first time Intel does this on desktop CPUs.