There was also the rush last year for I bonds in October or November I think because they would pay out a minimum of I want to say 4% or so no matter if the Fed slashed it down to zero again or not. That created a Treasury surge for sure I remember reading the website crashed because of the demand. 

Cje95

Undisciplined

econ

Tether's Circle of Death

I am not sure if we will see regulation to require it so to speak. Currently a ton of retirement funds hold these already and continue to purchase them. They are the target funds that people will by or that their 401k automatically puts money into for when you target to retire. 

Its my belief that that already serves to prop it up as it is. Stablecoins are just another avenue to find a place that is hungry for them. It will be interesting though that as the working force shrinks how it will affect US bonds because there might not be as much internal demand if that makes sense. 