Meetups should be a separate subreddit; they unnecessarily clutter the Discussion page.

Agreed. It's always bothered me how much space they take up.

Also, no matter how often the Open Threads will appear, people will still post Open Threads material in Discussion.

Well, things would most probably be better if some short guidelines, explaining what should be posted where, were put somewhere visible..

It would be better to use geolocation to see if the user is near a meetup and if so, we could show that in a little notification window at the top