This is what I would be curious about...also wonder if a RPi 3 would yield a higher FPS (if it's multi-thread enabled)
I doubt performance will be much greater on a pi3, its not threaded.. but it'll be more reasonable on some existing hardware you may already have running.. but after using Alprd a lil while I think a low traffic driveway might be doable on minimal hardware, the key is the FPS you get in daytime looking for plates (ie no plate in image), running in black and white 24/7 helps alot since its looking for high contrast squares, you dont need to process the same plate more than once really.. if it takes a couple seconds to read the plate thats no big deal because you wont have another vehicle passing that soon in most cases.
Plate detection is pretty reliable, and that alone could be used to trigger some alert/notification even if a read is not that good