And if you use "x" in some way that isn't allowed by the new type, you will still get a compiler error; although the error will be on the line where you use x and not on the line where you declare x. The compilers I've used (Visual C++, GCC and Clang) will tell you where x was declared in the error message.
Yeah well I'd rather not rely on 'chance' - if I would, I wouldn't be using C++.
I don't see how one can reasonably argue that type conversion is like 'rolling a die' - well yeah, if you use auto all over, it can be, which is my whole point. Next thing we'll need unit tests just to make sure a type change in place A doesn't make part B fall over - just like in scripting languages. Judicious use of auto to make iterators less painful to type; OK. 'auto' for types in templates where you don't know the type yet - that's a genuinely useful case (although there aren't that many cases where it's useful). 'auto' for every type just because that way you don't have to think about types - recipe for disaster and source of unexpected bugs, imo.