about G2 bus

[cybdyn]

yeah G1 IDE is most simple device)))
as prototype for developers and supporters it's not too expensive.
"CPLD + memory buffer" can be replaced by fpga with internal buffer RAM (~30..50 kbytes, enough for DMA frames). but maybe you meantioned about memory expand - like additional SDRAM 32..64 MBytes?)

no sure about Ethernet soultion, what IC to select : like mcu ARM + Ethernet , or discrette IC.

Advantage of such device could be Plug&Play solution. PCB measurment could be fitted to the case of popular useless Modem device.