First a fix: I wanted to write "but I will NOT commit crap there of course". Nasty errors
I agree with you basically about using the existing code. I was rather anticipating the practical problems that happen inevitably when creating code based on some other (not finished) code.
Sometimes you need to change the other code. If you send a patch for its maintainer and wait until he finds time to look at it and commit, your own work gets blocked for many days.
So, in reality you change the code without asking its author and then experiment with it. That is a fork already. And if many people work on the same code, also the forked part must be copied to the common repository. There is nothing wrong with it. Many of the experimental features will be thrown away and later the efforts can be united.
I didn't propose a competing forked solution but more a temporary fork for pragmatic reasons.
The GUI frontend may indeed be easy. But, there were also high-flying ideas with cross-compiling etc.
I don't know enough details yet to know how much work it is.
Juha