We have the current Farmduino version (included with v1.3 kits) available for sale now. The main improvements there though are with cabling/connectors, not with performance.
The next iteration of Farmduino does not yet have a release date, as discussed in this topic. The main advantages of the next version are the encoder co-processor (allowing for faster movements without missing any encoders pulses), the switch to 24V (quieter and more powerful operation), and the connectors/cabling (when compared to RAMPS).