Bitcoin should be widely used and widely accepted, even if it doesn't replace fiat, no big deal, as people who are comfortable with bitcoin, will never use fiat.
I 100% agree with you here. Bitcoin doesn't need to replace fiat outright - there will always be certain people who will always want to pay in cold hard cash. For example criminals, who are now switching to bitcoin a lot, will still be large users of cash. Similarly older people or those who aren't trusting of technology will always want to use cash. However I agree that bitcoin becoming more prevalent and accepted should be happening, and indeed it is.