The Compute Module 4 exposes the same integrated Ethernet port, and a
PCIe lane in place of the USB 3 chipset (the latter being attached to
the former in the standard Pi 4B). This obviously allows attaching at
least one real GigE port (with a free choice of PCIe-based chipset) at
full line rate, without the intermediate step of USB. I think it
would be reasonable to include a small Ethernet switch downstream of
this, matching the connectivity of typical CPE on the LAN side. If a
PCIe switch is inserted, then a choice of Mini-PCIe Wifi cards can be
installed, with cables running to the normal array of external
antennae, sidestepping the problem of USB Wifi dongles.
I would hype the heck out of a router-style carrier board. I'd even buy a bunch myself, for that matter. I used to make good money by putting OpenWRT on cheap routers for small businesses.
I've had good success chatting with Eben about Hackaday articles. If this were to become more than a pipe dream, we could reach out to him, to see if the Pi Foundation had any interest in backing a Pi router carrier board that beats bufferbloat.
--Jonathan Bennett