Retirement is an interesting point. However, there aren't any guarantees that IRA and 401k rules will stay the same. I guess that may come down to how far off retirement is. 

With fedimint and cashu I think people talk about a system of automated withdrawals (automated bank runs) which are much easier to achieve than real bank runs exerting a pressure on mints to stay honest. But it's not as certain as bitcoin's halving schedule, that's for sure. 

Scoresby

bitcoin

Is custodial bitcoin really worth anything?

I just remembered that ETFs can be used in retirement savings plans, and I see an advantage in this application. As for fedimint and ecach, I'm not yet fully convinced, as we have to trust the issuing entity. I'm not sure about ecash, but with fedimint it's not possible to verify the token supply.