I really like the MPA approach. To me it means building a bunch of mini SPAs. You can still stuff everything into a single SPA to deploy to a mobile app, but it gives you the advantage quicker first-time page loads and a lot of extra flexibility.
Compared to the Web 1.0 way of doing things where you POST and then reload the page, you're taking an API based approach so when a 3rd party needs to integrate with you - that part is probably done already.
A lot of sites use the MPA approach wrong though. They load the "apps", then proceed to make a whole bunch of asynch requests for data. In most cases, using a mechanism to inject in data when a page first loads makes everything feel a lot faster.
It's the best of both worlds: you get the speed of the old school web and the flexibility of modern practices.