My primary concern with this is that different applications are inherently optimized for the platform on which they were originally designed. There are some applications that have a very dense UI because there's simply alot of functionality that the program handles (think of a video editor, an IDE, etc). Trying to slim down those applications to make them reactive so that they will scale onto a phone or tablet just s…
Google redesigned all their desktop UIs to work with touchscreens in 2012, at the expense of mouse-and-keyboard users. Microsoft's Ribbon UI for Office, and Fluent UI for Windows 10 were both designed for touch first. Hell, even Ubuntu's Unity made huge compromises on Desktop in the name of convergence, even though no significant fraction of users ended up running Ubuntu on phones.
The original designer vision was for UI to adjust depending on the form factor of the user's device. What we got instead is "upscaled phone UIs everywhere", because programmers like to be DRY and reuse code. This is literally the tree swing cartoon.