I've been planning to make the switch to lithium ion power to achieve better range but there is one huge issue. Lithium polymer is 4.2v - 3.7v while Lithium ion is 4.2v - 2.5v so to achieve the same end of flight voltage as Lipo, you need more Li-ion cells. To get 3s Lipo performance, you need 4s Li-ion. This larger initial voltage means that motor rpm/throttle at the beginning of the flight needs to be limited to prevent burning the motor.
Essentially, what you need is a rpm sensor on the motor and a re-mapping of the throttle output of TECS to a requested rpm and some type of RPM governor that actually controls the ESC. This re-mapping needs to be active in all flight modes, including manual. One side benefit of this is that it would normalize the performance of the aircraft reguardless of the battery SOC which I suspect would make TECS perform better.