Instead of trying to reinvent the wheel (admittedly a new and shiny one), why don’t we just stick to the well proven approaches and design different UIs and front ends for different platforms? The bulk of the codes would go into the common business/security layers anyway. With CI/CD, each user would have his/her app with the same functionality but different UI for the optimal user experience without much headaches or additional burden.
To me the benefit is not to have a single application that works both with a touch screen and a mouse/keyboard. Rather, the benefit is to have a single filesystem that I can access with both touch screen apps and mouse/keyboard apps. This way I could for example create a grocery with a mouse/keyboard, then take my phone and check items off with a touchscreen. There are lots of things we rely on the cloud for that would be better served by a "convergent" environment imo.