I'm pretty optimistic that it will be bitcoin only. Moreover I would be willing to bet that the whole "no captial gains tax" thing is only extended to bitcoin and not alts (I think full no-cap gains tax is fairly unlikely though....most likely is they give a "de minimis exemption", so like no cap gains on transactions under $500)

My rationale for bitcoin reserve being bitcoin-only is: (a) Publicly traded companies are already rolling out bitcoin treasuries, there is no alt-coin treasuries out there, (b) Elon has a bitcoin-only treasury in Tesla, (c) RFK has most of his wealth in Bitcoin. (d) Lummis the bill sponsor, has been pretty much bitcoin only.....

Then there is the deeper strategic rationale, it would be foolhardy to adopt a shitcoin into your reserve and then vitalik prints a few million extra coins and dumps on your reserve. That could have real national security implications in coming decades if that were to happen.....

The howie-test for all its criticisms is actually a decent benchmark to protect investors (namely that its sufficiently decentralized and there is no single party that controls the investment). I think that century-long litmus-test will continue and bitcoin will be the beneficiary.