Well it is not a huge super unit, rather tiny and small, you can only build one per planet and also only if the planet is about to be abandon. Mean only extractors and generators to be left there for the income. The unit is self charging so needs no energy. What does it do? Well simply it cleans up the place recycles leftovers and wreckage. (But dont call it Wall-e, because of ™, ©, ®) but thats exactly what i think of.
Though I enjoy the idea, i don't really think it's necessary. I'd just throw my KEW at the abandoned planet. Scorched Earth P.S.: Someone please opens a topic for uberunits. Or we will have 100 threads in two weeks all filled with ideas about new units.