Earlier quoted context omitted.
What you suggest could work, but I'm not sure how useful that would be in the end when you still have to declare the type for fields initialized in the constructor. The var keyword inside methods covers most cases of using variables. A "var" keyword on the field level would cover less than half of the cases. Plus, you'd have to add a new keyword to do it as "variable" doesn't quite fit the meaning. Just not sure how…
You'd have to make special case syntax for it and it would just feel bolted on to the language. Plus, tuples lose their usefulness if you have to declare its type to pass it between methods. I think it could be OK even without return type inference on methods. Imagine you could type this: (int, bool) TryParse(string str) { // do stuff return (num, success); } That would be clean enough.
But once you get over that mental hump of seeing a new in front, it really starts to make a lot of sense. A tuple could be considered a value type and treated similarly to int or string literals. Very cool.