If you take a look at the way the industry is heading it won't be long before we are back to Steeple Jacks. One Man tied on, fewer components = minimal risk.
System will be the long term way forward utilizing ledgers/standards with welded on fittings (Cuplok/Layher etc)
Not sure what the best way to tether these would be, don't think I would want a 17kg standard tied to my belt if it fell over the edge?
Tethered fittings a valiant effort and a way forward but not sure how practical in the long term?? or the practicality on every job?
Hats and spanners etc can't see a reason not to tether them, that said I am not using them every day on site so can only comment with the best of intentions.