I would say some of the most promising work right now is in quasi-direct-drive actuators, basically low-gear-ratio brushless motors. Standalone electric motors are basically linear in terms of electrical power->torque, and even with a gearbox, provided the gear ratio is low enough, you can assume near-linear behavior. Brushless motors tend to be easier to design around specific size and shape constraints, and often run slower than brushed.
The "secret" to a lot of this actuator work is that outside of highly repetitive industrial tasks, actuators are rarely running at full power so you don't need to design them (and their cooling) for continuous max power operation. Somewhat like human muscles, you can pick smaller motors and/or lower gear ratios that cover the normal cases, and still be OK with rare overloads so long as the overload isn't long enough to cause overheating.
