Written works have had sarcasm, irony, and related forms of wit for as long as they've existed. While people might miss the mark, it doesn't mean we should just give it up as impossible just because we're now writing comments online.

And it probably says more about me than the writer, but I always cringe when I see /s since it seems to be implying "Hey, in case you're a bit slow, this is sarcasm. Glad to help."

Sarcasm is by definition kind of elitist. You get it, and you're in the cool group, or you don't and you go on your way. It's a puzzle to solve. Removing all uncertainty removes its fundamental essence.