If Bitcoin is global base money, then I think its risk-free interest rate is simply fixed at 0% as a result of it being fixed supply.
If you’re seeing a positive rate, then that’s reflecting some degree of risk, eg that your counterparty won’t actually give you the bitcoin in future. After all, if the bitcoin were locked in on-chain already, your counterparty isn’t getting an advantage, so why would they pay any premium at all?
In this case, I think significant risk comes from the question of whether the sharechain pool has any hashrate in future, or if fees/block reward drop below expected levels. In either case, your hoped for funds and interest won’t be available when you expected them to be.
There’s nothing wrong with that of course, it just means this system isn’t discovering Bitcoin’s native time pricing, but rather providing an insurance/continuity feature for mining payouts, which is probably more practical and immediately useful anyway.
IMHO, anyway. And it’s economics, where supply of opinions is always greater than demand.