I know that you're not suppose to run the starter for longer than 30seconds, but why? Shouldn't a starter be strong enough to continuously be used? I mean isn't it simply an electric motor? Is the reason for this is because they're using a an electric motor that is not really intended for the job in the first place? I was thinking that one could theoretically put a more robust electric motor, run a fuel cutoff switch and then run the "starter" which would basically act as an electric motor, therefore powering the transmission/engine.

 

Starters are high torque electric motors. They draw a tremendous amount of energy over a short period of time, so extended use is not recommended. High torque motors also generate a lot of heat and a starter housing doesn't have an efficient cooling system.

Your idea could work, but it would take quite a bit of energy and a large electric motor (that may be very difficult to mount in the OEM starter location).