As far as messaging apps, they're all technically there - the best kind of there for the crowd that this would interest. Spinning up a Matrix server means maybe a days work for this crowd, which allows (and I currently use it for) Whatsapp, Signal, Telegram, and more. Even better, due to constant improvements by Matrix, the server is only getting lighter and your options more varied with things like Construct [0].
Email is there - one only really needs to ensure geary is set to scale to the phone screen. As far as gMail, I'd question what the overlap is between "Privacy conscious enough to use a Pinephone" and "Uses gMail instead of anything IMAP".
That only leaves navigation and social media. For the former, I've used the mobile site in-browser on my Android phone that the Google Maps app was too heavy for. And for both on the Pinephone, especially the pro, Waydroid [1] is getting closer to closing the gap.
To be honest, I could see it being mainstream for geeks within two years. Though that's unlikely what you meant by mainstream - which I think we can agree is several more years away, if ever.