got bored and did some pictures of some ideas.
first one is for adding color code for aliens showing what kind of alien is there. lets say that soldier is green, scientist is yellow, etc etc... or they could present their toughness. i think this could bring easily "without-much-working" (i guess) a lot more variety to aliens by re-texturing the alien model Uvmaps. tho on the downside is, there would be much more images added for xenonaut, basically from same alien.
for second, is quite familiar to all... how about bloodtracks for the wounded? loved this concept in jagged alliance
and for the third... thinking twice, well this might be quite dumb idea and overpowered, but how about aerial support for the ground combat? just have a look at the picture, it has AH-1 Cobra supporting ...tho, it wouldnt need to be helicopter, could be a airplane also doing gunning raid from air or bombing... allmost can see the vulcan fire coming from the sky and high speed velocity shadow from the passing plane in the ground lol ...but yeah, overpowered.