Yes but where ?
Assuming that you can create a distributed coherent cache ( which EMC / NetApp has been claiming is impossible for the last ten years) then where would you put the SSD cache ?
On the motherboard ? How would the local cache software communicate back to the remote array, how often would the cache update ( EMC updates their Flash cache once per day ). This would most likely use a kernel driver in the OS e.g., VMware to use the cache.
On the CNA / HBA ? And make it part of the storage understructure would require support in the driver ? At what price would this highly custom piece of silicon, that would be bathed in Unicorn Tears and individually blessed by a virginal Tech priest as it left the factory ? I'd expect it to be orders of magnitude more expensive than the Fusion-IO product. Fusion IO is a a goodish flash drive built use the PCI-E bus in certain computers - but an entirely custom CNA with Flash and handy CPU/Software is quite different.
More answers than questions here.