What, precisely, are you looking for cryptocurrencies to “show” you?
Transactions work today. Plenty of people use them for exchanging actual value, quickly and anonymously (or pseudonymously) across the world.
> If cryptocurrencies are so good at transferring money what's stopping them from replacing existing solutions?
Why would the financial industry do anything to encourage the adoption of crypto? It strips them of their power. They rely on you keeping and sending money with them - the democratized platform of cryptocurrencies are a potential threat.
> Literal billions have been poured in the tech
Sorry, billions have been poured into a worthless speculative market. The developers are not receiving billions, they are still volunteers. And yet there has been a massive amount of development in the crypto space over the past 12 years. NANO enabling instant transactions, XMR allowing for privacy, etc.
> how long it'd be before cryptocurrencies actually delivered on that mythical "tech" and we'd get actual mainstream real world applications […] Can I get an update on that?
I ask again, what exactly are you looking for?
In terms of real-world usage, well, crypto has been used for years. Drug/Darknet markets, for one. Ransomware for another. These are stress-tests for any currency and prove that crypto can work to exchange value in a real market setting.
Further adoption is really up to people, and it will likely happen anyways as the technology improves. A lot of work has been done, but there is a long way to go.