Re: Q: Why no PCIe ASIC miners?

Agree with OP.
An PCIe ASIC card would be sick, I would buy for sure.

Let's assume that Chinese engineers can take one of the boards with ASIC chips and make it compatible with a PC via a PCIe interface. The ASIC uses powerful fans to cool the chips. Will you turn your PC into a noisy monster?
Such a board will economically lose to ASICs.

None of that applies to using ASICs in a custom system vs using ASICS with a PCie (or USB) interface in a commodity system. ASiCs are ASICs no matter how they are used.

In this I agree with you. ASIC is a standalone device and does not need an additional interface, except for connecting a LAN cable. If we connect some kind of mining device to the motherboard, then it will be an analogue of a video card or FPGA.

One negative is that new motherboards have fewer PCIe slots and more m.2. m.2 to PCIe splitters will be needed for the next mining bull when and if it happens.