Controversial opinion.
I love Bitcoin the currency, but IMO a major barrier to adoption has been the community's reluctance to embrace "off chain" payment systems. Bitcoin's network is simply too slow and expensive for the majority of day to day transactions. And there are fundamental reasons for that which can't be fixed with a fork or an altcoin. It should be used as a settlement system, for moving between payment systems and for large transactions (e.g. Coinbase -> Hardware wallet, Hardware wallet -> Pay credit card bill, Kraken <-> Binance, etc.).
Now what if Visa added BTC as a supported currency? That would be big for adoption. Consumers could pay their bills directly in BTC. Merchants could receive BTC from Visa. What if some entity (El Salvador?) issued BTC backed bank notes? BTC could be used just like cash. Basically, all criticism about the Bitcoin payment network would become moot. But the "on chain" system would still exist when you need it and the currency would still retain its important properties.
Is the above vision still considered taboo?
I think what you are trying to say is pretty much the concept of the lightning network too, as far as I have understood it aims to creates swift routes between nodes off chain thereby reducing the instances of transactions going on main chain making transaction more speedy and also less expensive. Also VISA is not at all needed in this whole process, LN already has a better concept than VISA could ever pitch in and moreover all of it would still be decentralized.