Hey folks,
Dual AGP slot boards have been made but it was a deviation of AGP.
Like AGP, the slots have access to system memory for SCSI controllers and the like.
The problem with dual "AGP" slots is bus loading and O/S support. I think it was super micro and ALR that made a "beta" dual AGP board. They had IRQ errors and multiple devices contending for bus time.
Having more then one device accessing the memory bus at the same time is a disaster.
I also saw at a design/R&D for ALR a dual in line PCI bus arraingment. It allowed "on slot" memory accessing for caching hard disk adaptors and the like. Now, its highly propriatory and of limited use.
New bus designs are "just around the corner" and should be apearing within the next 12-18 months. Also will be the "rouge IRQ" system board which utilizes claimed but unused IRQ time for devices. This is in beta as well.