soft wadi
I think it would be better to describe an activity you think would work well and be thematic for rewarding ~30k/hr Agility XP AFK.
No offence but a gnome treadmill sounds a bit ridiculous. I can't really imagine seeing a treadmill in the game - I generally wouldn't expect to see gym equipment in OSRS.
I don't know what you mean by "incorporate into Sailing activities". I'd generally expect Sailing XP from Sailing activities. You'd have to give some example of an Agility + Sailing activity for that to make sense, I think.
Agility boots have been suggested a number of times. It's a fairly controversial concept. I think at best, you'd need to find some way to balance it (and maybe it would end up being 12k/hr); but at the very least, it would make sense to make that a separate, dedicated suggestion.
eager tundra