There's some gain to be had in terms of efficiency, but not much. Induction motors are I think generally approaching 90%, and SRIPM-type motors are in the mid

There's some gain to be had in terms of efficiency, but not much. Induction motors are I think generally approaching 90%, and SRIPM-type motors are in the mid 90's. Probably the biggest gains going forward will be around improving the ratio of power output to weight, and reducing manufacturing costs (of both the motor and the controller). Maybe also increasing maximum RPM and improving durability, for whatever application where current motors aren't good enough. It might also be nice to have more standardization and modularity. In the EV conversion world, there's kind of a defacto standard of motors made specifically for conversion mostly using a B-face with a 1 1/8th inch shaft with a quarter inch key slot. That helps a lot, as you can buy a motor from one company and a transmission adapter plate and coupler from another company and have pretty good odds it'll work. There are apparently ways to get almost any motor to work with almost any transmission, but that usually requires custom fabrication. (Obviously you can also ditch the transmission and just connect the motor directly to the drive shaft or transaxle or whatever. I don't know much about that route.)