Android/ChromeOS and iOS/MacOS are already moving to this direction for these classes of apps.
It doesn't work so well (or is more difficult to execute well, or at all) on apps with very dense UI - video editing, 3D design, IDEs, interface design apps, CAD etc
An aside - I'm not sure I'd use GTK+ for this. Why not Qt, or something like Flutter?
This is why ubuntu phone tanked. Trying to be too smart and centralizing. Librem5 phone will probably succeed on this but not for the reasons their marketing people think (convergent apps with magic! ha!). PureOS will be as irrelevant tomorrow as it is now. But their phone, being a proper linux phone like android never was, will have some small chance of success after the community buys into it and start porting a decent effort to the applications.