The best case scenario for bitcoin is it becoming the de facto monetary standard, meaning there would be no reason to buy or cash out, as everything would be priced in bitcoin.
Bitcoin will never replace current fiat money as it is inherently flawed: price fluctuate too much, and favor early owner of it.
These aren't flaws, welcome to economics, man. Once bitcoin gains enough things will be priced in BTC, so fluctuation won't be an issue.
Deflationary economics benefit the savers, while inflationary economics benefit the spenders. Just because bitcoin's economic model isn't something you're used to or like doesn't mean it is 'inherently flawed'.
So you mean, like, people will not waste nature's resources for things they don't really need? Oh, what a tragedy!
Only people trying to cash out need people buying in. If you were really invested in the long term you'd rather people not buy in so you can buy more at a lower price.
Bitcoin also has fees. The only reason the fees are lower than credit cards are because people in China can afford to burn electricity at a loss just to turn their Chinese money into anything else.
You still have to pay taxes on the capital gains. And you can't pay taxes in Bitcoin.