As for the real physical economy.. that is a bit more tricky, but at least where I live, even businesses that pay taxes, would still prefer taking cash, so why can't Bitcoin win if it had as good UX and as good liquidity as cash?
Discussion
You need stable prices first, everything else is a gimmick.
I again disagree, but maybe because I am much more of a saver than spender.
But I really do think stable prices are not that hard nor do they need central authority, at the end of the day stability of Fiat is just a small part of businesses concerns, the rest is hedging against volatility of prices of inputs, which is not done by central planning, but through futures, and I see no reason why can't there be Bitcoin denominated futures for the inputs of the digital economies.
There is also over collatorization and somewhat trustless oracles like the UTXO analysis thing...
Anyway, I think it is doable, but I don't personally care about it that much, if you do, I hope you will work on it instead of thinking it is impossible to fix.