The line is out of action while deicing is taking place, but only for the shortest amount of time necessary.
That's what I'm thinking, yes. Although you could pump a lot of heat into the pantograph, and pair it up with a scraper at the same time.
It wouldn't be able to run line speed, but it would be reasonably fast, I'd think.
I've heard that one a few times before actually, it's not entirely unfair either.