+1 for the change but not for an extension. Here's why
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.
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.