One of the issues with that second bracket is there are not many cases that supports it. Mac Pro, HP workstations and desktop servers, and old, cheap looking, bent metal “DOS/V” cases has it, but modern “EATX” cases often don’t. It also cannot support too much weight.<p>Indeed, PCI standards were for adding interfaces to personal desktop computers after all. It does seem ill suited to host 450W cooperative sub-computers.<p>A more common approach to heavy expansion card is VME style chassis design. Off top of my head, NeXTcube, NEC C Bus, Eurocard uses this arrangement in consumer space, and many blade servers enclosures, carrier grade routers, and military digital equipments employ similar designs as well.