Most forklifts anymore have some sort of control system that is specific to that make/brand,and USUALLY needs maker specific software and programming to access it,they are not like cars where you can purchase a OBD II scanner at the local autoparts store to retrieve codes,anymore they need to be accessed with a computer and software and cables supplied only to the dealers that sell that brand.
as for drive by wire yes there are forklifts that have this type of system on them. As for limiting the speed on them you would need the program and cables only available to the dealers to access and change the settings on most of these trucks.