Maybe it's gimmicky, but I feel like you could get some interesting form factors with the CPU and GPU cards sitting back-to-back or side-by-side, and there would be more flexibility for how to make space for a large air cooler, or take it up again if you've got an AIO.
I know some of this already happens with SFF builds that use a Mini-ITX motherboard + ribbon cable to the GPU, but it's always been a little awkward with Mini-ITX being a 170mm square, and high end GPUs being only 137mm wide but up to 300mm in length.
Then each device can be a host, a client, at the same time and at full bandwidth.
The transputer b008 series was also somewhat similar.
For cases where there are other cards, yes there would more contention, but few expansion cards are able to saturate more than a lane or two. One lane of PCIe Gen5 is a whopping 4 GB/s in each direction, so that theoretically handles a dual 10gige NIC on its own.
I had envisoned a smaller tower design that with PCI slots and Apple developing and selling daughter cards that were basically just a redesigned macbook pro PCB but with a PCI-E edge connector and power connector.
The way I see it a user could start with a reasonably powerful base machine and then upgrade it over time and mix and match different daughter cards. A ten year old desktop is fine as a day to day driver, it just needs some fancy NPU to do fancy AI stuff.
This kind of architecture seems to make sense to me in an age where computers have such a longer usable lifespan and where so many features are integrated into the motherboard.
https://512pixels.net/2024/03/apple-jonathan-modular-concept...