I would like to push back here: this seems to be suggesting a fork-like situation, where we have two kinds of Haskell (fancy and non-fancy). I do feel quite strongly that we should be converging on a single language rather than creating splits. Or perhaps the suggestion is that we don't want these extensions on by default *yet*?
Responding to Iavor's point:
> I think these extensions convey useful information about the mindset you
should use when working with a specific code base, which is quite
different from working with ordinary Haskell.
I personally have been working with these extensions enabled for all my code for a long time now. I'm by no means a heavy user of "fancy types", I make occasional use of type families and GADTs to solve specific problems when they arise. But I'm not even sure what this "different mindset" is - I certainly don't feel like I have to think differently. Of course it's entirely possible that I'm just an unsophisticated user and if I understood how to think about the type system with these extensions my life would be better!
The one exception that does trip me up is MonoLocalBinds, I often have to supply a type signature when intuitively I didn't think I needed one.
Cheers
Simon