In reply to slackloaf:
As a climber, my instinctive reaction to this is that the rules climbers have come up with to protect crags are (vaguely) sensible and have evolved over years of debate, and that slackliners should consider that carefully before making changes to rock that can't be undone (i.e. even a chopped bolt leaves a hole which once was rock, and, as I understand it, on grit damage to the tough crust can damage the softer rock underneath).
A second thought is that why should slackliners care? Depends how much they think that rock is worth 'preserving' - which is often the argument used against bolting, particularly preserving a challenge for future climbers though. But then if they don't respect the natural environment, why would they feel so strongly that they want to slackline in it that they can be bothered to go to the effort of placing bolts.
I've slacklined a bit with climbing mates and have to say I've hardly ever seen other people doing it.
So at the other end of this, how big a deal is this really going to be? I'd have thought that highlining, due to the very nature of it, will never be a mass participation thing. It's not like bungee jumping, you can't just get on and do it, you need to build the skill. Then you need to have the guts and desire to do it over a big drop. Then you have to have the desire to do it at a crag rather than in an urban setting etc etc. To my mind, that's always going to be a niche pursuit.
So really, we're talking about a very few bolts on a very few crags for the use of a very few people. I guess the slackers could, if they feel so passionate about placing a bolt, just go ahead and do it. But just like sport bolters, they'll run the risk that if someone feels passionately anti where they've put their bolt, it'll get chopped.
So to avoid this, the sensible thing would be to bolt in a discreet way, which is unlikely to come into conflict with climbers anyway.