I'm going to describe this in terms of gold; as a metaphor, you can replace gold with any other non deflating asset. There's a limited amount of gold. If you could atomically store your cash as gold yet still pay with it directly through debit, then you don't really need cash. But man does not survive on gold; so you must spend the currency
By settle in value I don't mean settle on a precise fiat price. Because I'm thinking post-fiat. This may be idealistic, I know, but try to think from that perspective. By stable I mean the value of BTC shouldn't double every two months. Unless the goods it buys are becoming twice as cheap due to technological advancement
There may be weird implications of having your mortgage be in terms of an asset that's non deflating, where if the economy is causing wages to go down as cost of living decreases it can become infeasible to pay for one's house in a year. Two things: banks can come up with a bank-coin which should inflate in order to stimulate long term loans, & maybe people should avoid debt. I personally live with my only debt being my mortgage
So maybe BTC isn't a good currency to take out a loan for, but in that case if you can have the bank agree to a dogecoin loan it work outs. I only mention doge because it's an inflating cryptocurrency originally based on BTC, but ideally the inflating currency would be segwit so that one can make atomic payments to that currency with their BTC. Kind of going on a tangent here in this stream of consciousness but the core of this idea is that you can pay with BTC for something in a different unit, currently loans are in the unit of USD, but perhaps in the future loans will be in terms of a 'platonic housing price according to some index' unit