Every such transaction will likely be a cheaper and more economic benefit for the party that receives bitcoin. The purchasing power increases over time. And everyone will want to use it. Simple. I do not expect amazon to allow bitcoin. However, I expect bitcoin to be used in other parts of our lives in the next decade
So it is and will be! We are already witnessing it thanks to the desire we have made for Bitcoin to be accepted in our day to day.
I think we will move towards mass adoption if we propose it. Once on a local e-commerce platform, I offered to pay for a phone with Bitcoin and the seller accepted and we proceeded with the transaction.
This won't be possible no matter how we want it unless Bitcoin will be centralized in the future but that is quite sketchy still, at this moment. Fiat currencies are more supported accross the globe multiple time more than Bitcoin and other cryptos which could still be considered as something new. Thus, fiat currencies will forever exist and if there will be a bright future for cryptos, these two will more likely to co-exist with one another as alternatives. To put it simply, Bitcoin could be in mainstream but the support still to fiat will always exist, that's how powerful governments are.