I doubt that USA with their budget deficit and huge debt will buy bitcoin. sure they may hold confiscated BTC but it's not equal to buying new coins. there is an opinion that USA may follow the approach of Strategy and issue government bonds to buy more BTC. but this move could undermine the trust in US treasury bonds so it seems doubtful.

as for me good chances for bitcoin strategic reserve have such countries as Norway, Qatar and others with big budget surplus. Norway's Government Pension Fund Global has 1.4 trillion AUM. maybe they have indirect bitcoin exposure through ETFs but these sums are not significant. also Qatar Investment Authority has about $475 billion AUM and there wasn't information about their investments in BTC.

so my point is that countries with budget surplus could afford buying BTC in big volumes. besides Norway and Qatar it could be Saudi Arabia, UAE, Kuwait, Singapore, Germany and someone else with big finances. with all due respect to Salvador and other not so financially strong countries their volumes aren't significant but their example also matters.