I tried it once, ran out of memory debugging a template error as it blew up my terminal into a sea of jibberish.
Not sure why the parent is in gray. It's a perfectly valid and widely practiced approach.
How often it works out as intended is very much up for debate though.
For legacy codebases, switching the compiler is certainly out of the question. For everyone else, why do you think it would be an issue to use the C++ compiler?
Because the complexity seeps in through the cracks, and with the language comes a mindset; same reasons Linus is wary about C++ in the kernel.
Some say it works; I've never succeeded, even on solo projects.
I think this is the general style for the Godot framework. They use a limited subset of C++, avoiding STL and some modern features, and limited templates.