Regulation and control is basically what is gradually stopping integration.
Governments has the fear of losing grip in money policy, the flow of tax, and control of capital when Bitcoin turns legal tender. Banks and financial institutions happen to resist, reasons being that it disrupt their normal method. Meanwhile households and firms may approve of it informally, complete adoption requires the backing of government, global cooperation, with infrastructure as to take care of volatility and safety matters..
Well, some banks are now accepting Bitcoin deposits. Institutional investors and governments are also accumulating large amounts of Bitcoin. We already have centralized exchanges forcing users to comply with KYC to buy/sell BTC. With strict regulations in place, making Bitcoin legal tender should be a no-brainer. Especially when most governments are collecting taxes from it.
Like I've stated before, governments don't want to make Bitcoin legal tender out of skepticism. Doing such a move, would be a sign that Fiat's days are over. It's all about power/control. Which means, governments will stay with Fiat to manipulate the economy as they see fit. Legal tender or not, Bitcoin will survive for a very long time.