The CM4 and the Pi4 hack expose one PCIe lane, correct? Is it possible to use some sort of... port multiplier / switch / hub to run more than one PCIe device on a Pi?
I've been farting around with Friendly's devices. Several of them have 2x PCIe, which I'm using/will be using for persistant storage, but I don't think you could compare anything they have to the compute module, especially with respect to PCIe.
The RPI4 has a 1x lane of PCIe 2.0. Maybe you could split it into two 1x PCIe 1.0?
You can split it to two 1x PCIe 2.0, or perhaps even 2x, 4x, probably even 3.0, 4.0, with the right chip, but in any case you need a PCIe switch, and they will share the uplink bandwidth.