I was excited to see this project on HN today. I see a lot of value of Wasmino in that it runs in the browser: it lowers the bar considerably for starters. I remember when I started that the amount of different boards you could buy was overwhelming and being able to try things out before going in the rabbit hole of selecting the right components and boards might definitely helps out some software developers that do not have a strong background in electronics or electrical engineering and make them excited to work in the field of embedded software.
A side project of mine that has become more serious last year is quite similar (https://www.studiotechnix.com/). My tool has the same caveats as Wasmino in that the CPU is modelled as "infinitely fast" and only "time functions" progress time. It is inherent to the method of simulating software coupled to physical models of hardware. Even with these assumptions, simulation can uncover a lot of functional faults / logic reasoning flaws in the embedded application. Testing on real hardware is of course still needed, but iterating on your design in simulation is much faster than on the real hardware. And it provides an easy way towards test automation which is much harder to setup with real hardware.