Well, I am against the 2 codebase thing for C2, doing an app separately would be stupid (incompatibilities and bugs would be kind of multiplied), however I can imagine the idea of the html5 version, where you can either pin the different windows (like the property window or project window, or the layers window, like the way it currently works), or make them as side tabs, they would open when you drag them onto the center (thus, they would not be covering up the screen, and you can access them), some might say "not that convenient", stillnmore that not having a mobile version.
For the event sheet, I do not see a real problem on mobile, but even then, some people have tablets too so I see no reason of censuring one platform.
However it is just my opinion.
So in short, I am for the development of a html5 based version, to be fair I tried the webapp of gdevelop, and it felt good, not perfect, but good, and I am sure it is also doable for C2 (or whatever the name would be)