Have a look at the VSL [Vienna Symphony Librayr] Ensemble Pro 5.
It acts as a host for AU/VST/VST3/AAX Native/RTAS instruments....The software connects your main DAW to plug-ins running on your slave computer. All Midi and Audio are done via ethernet. You can use 32bit and 64bit plugs. VST3 supports up to 48 midi ports [ie 48 * 16 channels!!], and 768 audio ports!! Comes with Epic Orchestra - 9Gig orchestra sample library.
I think it would need backward compatibility. There is so much excellent 'old' gear you wouldn't want to throw that out. I believe copperlan doesn't actually solve the problem because it still relies on MIDI connections.
Software: Steinberg Cubase Artist 6.5.5 64-bit. Hardware: HP elitebook 8530b with W7 Home 64-bit Mackie Onyx 1620i - Steinberg Midex 8 - Steinberg CC121. Analog: Alesis M1 - Behringer Powerplay Pro-XL - Studio Projects C3 Instruments: Yamaha DTX750k - Yamaha MO-6 - Waldorf Blofeld. 3rd party plugins: Native Instruments Prism - Rob Papen Distort - Rob Papen Delay