I believe there would be benefit to documenting highlines for slacklining. We have a number of these in Colorado and we are putting more up. They are situated near some sport climbs we are putting up as well.
It is getting more popular and I would like to be able to search for them as a catgeroy instead of a string query against the free text fields.
Though I'm not in Colorado right now, I know there's a HUGE community of slack/high-liners (myself included). I believe that it would be a great idea to add as a forum, except I believe that this has come up before and since its not "climbing" then it doesn't fit the MP platform.
Nevertheless, I think that it could be a way for MP to expand its customer base. Although most highliners are climbers, it creates another group of people that would use the site and with them, the growing number of slackline companies and advertisement revenue. Sounds like an easy way to bring in more users just by adding a single category.