I had idea of having second Sectoid race that would appear later in game and would be on level of Ethereals. Some kind of variour caste of sectoids compared to scouts from the begining. All their soldiers would be these mechs. If you destroy it, out jumps armed Sectoid soldier so you have to kill each unit effectively twice. Medics and Engineers would be buffed too and they would have both Leader and Commander with psionics on level of Ethereals. Only the Navigators would be kinda weak. Also intead of cyberdisc, they would have those cyberspheres that would work similarly to cyberdiscs, only smaller and faster. Maybe armed with blaster :-)