I can't see how it would be possible to ban a certain type of clothing - you could end up with something as supportive as any shooting jacket by altering or adding pads to any old coat. Slings are easier - they can be used just for carrying and if the use of the seat is causing problems in kneelers then maybe just ban that altogether too.
I use a sling when kneeling, it's a single point which is always on the gun, but I would not moan about it being banned. The biggest problem I see (well notice) in abuse of positions is the slumped mode of kneeling position where the knee, supporting wrist and fore-end are all far too close together for legality to be even checked.
I may use a single point sling at the moment, but the elbow of my supporting hand rests only very slightly behind or on my knee, my kneeling position is entirely conventional and upright.
I use my seat under my ankle, it's folded under my arse but I don't sit on it; I've tried having the excess poking out behind me but I find it impossible not to push against it, which I feel gives me an unfair advantage so I don't do it, though it might look better if I did.
Before last year's championships in Italy I understood that slings were to be outlawed so I trained without one. The radius and pattern of my hold was absolutely identical with and without the sling, but with the sling the movement was perhaps slightly slower. For me the difference is slight.
lots of talk about various technical what-nots but nothing about guns and scopes - if we are going to start banning target related clothing why not butt hooks and hamsters etc.? A limit on the distance from sight line to the base of the stock would probably reduce dodgy kneeling positions at a stroke.
All in all I don't think there's too much of a problem, if kneelers had to be taken in an upright position rather than a slumped heap, which is impossible to even judge, then we'd probably be okay.