I got this idea from a post on the bnet forums and thought it through. Imagine a protoss carrier going red and a zerg spellcaster infecting it. It would grow a giant tumor on it and would fall to zerg control. It would retain its sheilds (they would still have to recharge) but have greatly reduced health that regenerates very quick like the roach.
The Infected Carrier would be able to produce scourge (the suicidal zerg unit) and have the option to crash down on the ground and explode to take out enemies. I guess that ability would be useful for taking out a lot of peons mining minerals or finishing off damaged buildings. And could also crash into lifted terran buildings like barracks or a command center.
Zerg players would get this ability researched at a high tier and it be costly in sp or even cost the spellcasters life.
Edit: Fine. How bout the same thing for battlecruisers? and the zerg could get infected terrans to commandier the carriers if the ship itself becomes infected. I wasn't taking about zerg infecting the pilots, but the ship itself getting infected with the infected terran's help (lore wise)
As for the unit iself, it would produce pairs of scourge 1 egg at a time thanks to a larva growing out of the tumor. It would take a bit of time for another larva to grow so zerg couldn't spam scourge unless they have 3 or 4 ships. Gameplay wise blizzard dudes can experiment and tweak to make it a normal unit, have a limited life (its time slowly counts down) or have its sp go down with every pair of scourges made which would kill it when it hits zero. I guess each ship should be able to produce 3/4 scourge eggs, and the scourge's attack damage could be tweaked. So players won't make scourge as much as they can and crash the ship then, the crash ability would itself take a lot of sp. Or simply be much more effective the more sp is left.
Another Edit: So it'll work for carriers and battlecruisers, and blizzard could decide to have this ability from a spell caster or have this as an upgradable ability for flying zerg units.