Few thoughts:

1) tax policy can be uncertain and expecting the government to not tax Bitcoin consistently for the next XX number of decades is a heck of a financial risk. That’s such a huge honeypot it’s hard for me to imagine zero taxes on any large asset forever. Politicians change and political parties fall in and out of favor with every cycle. Trump is not our last president and an anti-Bitcoin president in 20 years if the masses get jealous is totally possible, who knows.

2) Could always do some in and some out of an IRA. Doesn’t have to be all or nothing.

3) you can do an Unchained IRA and keep self custody. Zero custodial risk