I would love to see the web vault as a PWA. The web vault is difficult to read on mobile.
I believe the following request should be merged with this one, as well:
Making the website into a PWA would be a great way to make the web vault mobile friendly, as mentioned in the OP.
Making the web vault as a PWA would not only improve usability, it would also give an installation option for those on low-end mobile devices and Chromebooks.
A PWA would also give premium users better access to the provided tools, something I believe is not even available directly in the Android mobile app.
As an example of what I mean when I say PWA, visit https://twitter.com on an android device using Google Chrome. You are presented with an easy to read page, and given an option to install the PWA.