As i remember there was a topic about this but as i remember it was about texture of alien, as changes upgrade skin also changes.
But my idea is little different to that one. Is there a way to merge a part of the upgrade building to the alien who is using the upgrade.
Like when you pick regen upgrade, you'll get the specific part of the buildin related with the regen upgrade
It maybe look like a visual change but it can be eventaully changed into a tide changer. Like there is a fade blinking around everywhere and it has regeneration for instance,
if you're lucky or have a good skill for aiming you might hit the merged upgrade part and hinder the upgrade for a short time maybe. Of course if can this be applied.