The disadvantage of the proposal is that it requires manual work from an asker or a 2k+ person and it may not work for all types of questions.

It's not that a "late answer" is "invisible", it's just hard to notice. Answering a question does push it to the top of the pile again at the homepage. The original asker will also get a notification next time they log in.

But generally, yes, it is a weakness of the Stackexchange software that later answers don't receive much attention. This is in part of result of design decisions made for Stackoverflow --- there's a much great sense that for programming questions prompt and early answers are more useful than later ones.

I'm having trouble imagining a mechanism to make later answers more visible, though. "Paying" the server some of your reputation, to keep the question high on the front page, until it's received a certain number of views???