Completely do-able. Depending on your setup you can do it a few ways. In my car, I'll likely splice the 5v VSS signal wire, send it to the arduino and calculate speed that way. If you have an ECU or data-logger that supports can-bus, and you know the messaging protocol you can just send the data over the bus to the arduino and then on through to the EPAS. Unfortunately I chose a Holley Terminator X and Holley regards their messaging protocol to be proprietary (likely to lock you into their add-on ecosystem). You could snoop their can-bus and decipher their messaging. If I would have went with Megasquirt its all documented.
If you have a stock cable driven speedo, you could buy one of the digital speedo cable extensions and send the output from that to the arduino.
