The ability to drive 7mm locos depends on the stall current of their motors.
The current locomotive control unit and battery have been designed to handle stall currents up to 500milliAmps and for some small 7mm locos with high quality motors, this will be perfectly adequate.
However, we are currently developing the next series of components which, apart from ones to fit in smaller 4mm locos, will extend to larger motors with stall currents of initially 1.5A and 2.5A.
However, we are aware that many of the larger 7mm locos have stall currents exceeding this, so the development after next will concentrate on the much larger currents.
We are aiming to have the next series available in Spring 2017, and we will then start work on the larger current components.