As I've grown in modding experience, I began thinking yet again about this faction of melding units, called Virons (from the game Ground Control 2). They've utterly fascinated me and were a mini obsession for a while. Their main thing was units would meld and form another, separate type of unit, which was the only way to get it. You could unmeld to go back.
Before shared caps were removed, I was intending for the basic unit and the meld result unit to share the same cap, so you can't max out on both at once, you have to switch. Now I don't know how this is possible.
This is minor really, and I don't expect any work to be done on making it doable. There is the possibility of them simply being a unique mercenary force that is granted to the player. Then the cap doesn't matter, because you can't build more. Might be two Neinzul with a Warhead there, to make a bizarre variant of a common phrase. Though the possibility of being able to make them into their own faction that you can capture and use is still intriguing to me, though I'm semi-terrified of having to upkeep something much larger than simple XML mods, if this is considered for the main game.
EDIT: One additional thing! Can something be made immune to engineer assistance? I wouldn't want the units melding instantly because of them helping.
