+1 for the change but not for an extension. Here's why
1. I remember when I was new to Haskell, having to add $ confused me a lot. It caused a lot of frustration, some errors I didn't understand, which didn't help me realize that $ was needed. I still vividly remember the pain....
2. It seems the change is fully backwards compatible and it does not prevent people still using the old style if they wanted. I would make it a default, not an extension.
3. In order to verify backwards compatibility, I would generate Core output for all of Hackage with both the current and the new compilers and check that Core remains identical. That would be a conclusive proof to me.
4. Regarding the other mentioned extensions like multiway if, etc. they should become default as well because they are backwards compatible as well.
5. The only reason to guard changes behind LANGUAGE pragmas should be when they are causing problems with other extensions.
I too feel that Haskell community is becoming more and more conservative. I believe there's still time now to make the language as best it can be at the cost of loosing backwards compatibility. The rapid improvements in the language is what attracts me to Haskell.