More Intelligent Eclipse "Open Call Hierarchy"?

Eclipse should already do this. If you want to test it, go to your A interface, select the x() method and run 'Open Call Hierarchy' on it. Do the same for your x() method in interface B. You should get different code locations, unless you have a class which implements both, which you should never do. Doing so won't break any compilation or execution, you will just be doubly declaring the same method signature.

I have tried this with a frequently-overridden method, toString(). When I right-click on it and choose "Open Call Hierarchy," Eclipse happily searches through my entire workspace and returns all references to that method signature.

I often rely on Eclipse to go the opposite way: I select a method invocation and press F3 to Open Declaration. But I don't think Eclipse is able to go the direction you want, from the declaration to the calling reference.

It may help to remove "Potential matches" from the search results. Try this:

Preferences -> General -> Search

And check "Ignore potential matches".