The sling has occasionally caused contention in bfta rules debate. Most recently there was a proposal to ban the use of slings except for using them to carry the rifle. This was rejected with the sensible argument that a sling offers a cheap (accessible to all) means of steadying the aim compared to all the other pricey gadgetry.
As others have alluded to slings are not commonly used in FT and only a few times have I seen single point slings. As is well known Simon A uses one very successfully.
The problem with attaching to the jacket has wider implication to what may develop. Tales from abroad include shooters strapping themselves together and screwing support aids from the rifle to the jacket (honestly).
I think that the use and attachment of the single point sling has not been fully explored at bfta committee and this is primarily because of the scarcity of its use.
I'd like to hear from users of single point slings (from any discipline) to inform how they are used and if this has implication for field target.
Unfortunately your question comes after the publication of the AGM agenda but the sling may be considered under any other business. Hopefully those at the meeting will have knowledge of any previous debate on the subject.
I agree that the rule looks like a cover all and description of the use of the sling should be specific regarding its attachment.