Are Progressive Web Apps possible with Xojo? My first instinct is absolutely! But I’m not sure if I’m missing something.
I call that simply well designed web apps. You can put as much hoopla in a Xojo web app as you want, if you know what you are doing 
But xojo web apps dont work offline when on public internet.
You can. Aloe [ https://aloe.zone/ ] plus something like the following github project would work great: GitHub - oliverjam/minimal-pwa: A verbosely commented minimal progressive web app would work.
@Tim Dietrich and I were talking about this yesterday, but most of our projects rely on live data. I think it could work well if your project had to work off like, like on a flight. Aloe, as it stands now, allows you to load data, fill out a form offline, and then go back online before submitting. If your app relies on an internet connection to auto save on each field change like Xanadu [ http://xojoxanadu.com/ ], it might not be worth the effort to go with a PWA.