It is unlikely that BTC will become cash, because BTC is still inadequate to put them into circulation in the consumer market. Too many people do not know how to use BTC technology
yes that's right, the lightning network is still not completely perfect. maybe 20 years from now it can happen. maybe

it looks like bitcoin will not replace paper money and can only be an alternative payment after the lightning network is stable, because there are still many people who don't understand bitcoin and also bitcoin prices are very fluctuating, maybe people will be afraid to save bitcoin.