The only problem why I don't think Bitcoin will be widely in the future is because there's a lot of new and existing crypto that has a better feature than Bitcoin. No one can assure the value of BTC because there is no valuable things such as Gold or USDT backed its existence. Only speculation on the price is what keeps BTC grows overtime.
Bitcoin is a popular asset and trusted by many people (its user) and increased adoption is a form of support for the development of bitcoin itself. I think bitcoin cant be affected by the volatility of other asset such as gold and also fiat or the stock market because I think bitcoin is an asset that has its own foundation without any authority controlling it.
Besides that, Bitcoin can't or might faced hard time on co-existing on the financial system because they are completely opposite. The current financial system is centralised and BTC is decentralized. We all know that in terms of financial, It must be centralised so that government can control all taxable money. As you can see, the goal of most big mover BTC related company was to register an ETF that will represent BTC on stock market. It means that BTC direction towards to indirect centralization.
I don't think that bitcoin will be a centralized asset in the future, although in term of usability it could still be the same as other centralized instrument. Bitcoin cant be controlled and can only be regulated based on the laws applicable in each country.
So far, bitcoin is not an illegal asset used by its user even though there are several countries that have severely restricted the existence of foreign currencies such as Argentina and Russia. I can still use bitcoin as well as fiat whenever I want, both have weaknesses and strengths and I think there is no problem bitcoin and fiat coexist just because not everyone know about bitcoin and how it works and they still need fiat.