"Time will tell if a NSS has been built up here over the years by MMs, IMO."
While that is probably true (that "time will tell"), the solid fact implied in yours (that we can't tell now) IS clearly true... and that fact provides a proof that there is a large problem that exists in our markets.
The markets should be transparent enough to enable knowing what the REAL balance between demand and supply of shares is, at any point in time... in real time. The only reason there can be for obstructing awareness of that reality in the true balance between demand and supply... in any time frame... is a desire to enable the practice of fraud based on that lack of market transparency.
That is particularly true now, when technology makes that easy, and enables us to participate in real time auctions, live, 24 hours a day. REAL auctions, without a need for any "market making" intermediaries manipulating prices, and whose function only works to obstruct our view of the real balance between supply and demand, interfering with proper price discovery.
If the markets we have now cannot enable that sort of transparency, we should create new ones that can.
If the only reason MMs wanted to allow short sales was to "facilitate proper market making"... then there would be no reason to have an interest in enabling any lack of transparency, as the market making function would be transparent, too, ensuring that the market price always properly reflected real supply and demand.
Instead of full transparency, giving all market participants full awareness of the real balance between real supply and demand in the market as public common, what you have now gives us absolutely no way of telling what the real situation in supply and demand is.
Maybe, as you say, time will tell... but, there is no reason anyone should ever have to wait to know what the balance between REAL supply and market demand for shares (or anything else, like ounces of silver... ) actually is.