Clojure's emphasis on backwards compatibility is commendable, but keep in mind Clojure is still a very young language ( only about 10 years old ) so there isn't much backwards compatibility to worry about.
Maybe, but this was true even when Clojure was younger still. The language changes are overwhelmingly additive; Hickey places great stock in not breaking existing code.
If you want to demand perfection, then Clojure isn't going to meet your standards (what would?).
The issue here is that, based on the way they (particularly Rich) talk, we can expect they will not do Bloody Stupid things like the old Python 2->3 changeover. Things like big, breaking changes that require architectural changes to keep current, or break all the available tutorials.
If the problem can be fixed with a macro or single function (like a change to plus behavior) it is an irritant, not a threat to productivity. That is not a concern.
I don't see how a change could be much more minor, honestly.
It is a breaking change, that sort of change could introduce bugs into existing codebases. If that matters, you can't upgrade your Clojure version without careful change management anyway.
It isn't like reduce is being depreciated or something. I don't need to change how I think about the language.