This a meta-meta question. When a question on meta is tagged discussion, I take it to mean that the point is to discuss, with maybe not a final goal of having one "answer", although with that possibility if lots of people agree. Should responses to the "prompt" go in comments or in "answers" even if they're not necessarily answers?
Answers on discussions can be almost anything that pertains to the original point. Completely off topic answers will be removed (flamebait, unrelated agendas, stuff that's not common on UX anyway), but pretty much anything else is fair game in discussion.
It really depends on the "question"; if it's really a question asking for solutions, "answers" (the SE term) will often be the form of answers (dictionary term). IF it's something like "give me feedback" or "I think X is a problem" then your "answers" (SE term again) might just be supporting/opposing opinions.
Generally speaking, anything too big/unwieldy/important to be put in a comment should instead be an answer on discussion questions. As long as you're remotely on point your answer probably isn't going to be deleted or anything.
Now, as far as "final" answers; some discussions welcome them, some don't. Sometimes the community comes to a clear consensus or at least a majority, and in that case "accepting" an answer can be useful. Generally speaking though votes (and argumentation) mean more on Meta than the accepted answer checkmark. But that doesn't mean the checkmark is entirely useless.
Now I'm tempted to mark this as the accepted answer, which sort of disagrees with my initial assumptions when writing this question. I'm so torn! :) May 16, 2013 at 23:33
1@norabora that's actually a point I forgot to address; "final" answers! May 16, 2013 at 23:35