@ David Rahaby ... as you say you are long-minded (and I believe you) have you considered just how much the management fees will eat into your BTC over the years? IIRC correctly the annual fee is 2% of NAV and it is taken in BTC not USD, so if you start with 100 BTC ...
After 10 years = 81.7 BTC
After 20 years = 66.8 BTC
After 25 years = 60.3 BTC
[...]
Meh, I'm out of my element here (retirement fund
and in the US), but isn't this a bit of a simplistic comparison?
As I understand it, the relevant point here is that GBTC is compatible with a Roth IRA, which is (intended to be) tax free, so depending on how capital gains for "raw" Bitcoin holdings are (and will be) taxed, and whether you are planning to pay those taxes (or, if not, whether you get away with it), those "2% per year" could either turn out to be a lot, or not that much.
Someone more knowledgeable on the topic, please feel free to correct me if the above is factually wrong.