The Turing test is not a definition of intelligence. Turing explicitly suggests the test in order to replace the question of the definition of intelligence. The test is most definitely a test, in the sense that it provides an estimate, rather than a clear cut definition.
While the limits in this case were admittedly rather strong, this does not form a fundamental objection to the test. The bar can be set progressively higher.
What is the limit, the ultimate height of the bar, then? A test that requires three score and ten years with a 50% success rate? Longer? The problem with the Turing test as a test is that it is always possible to game it, to create a system that can pass with any set of feasible limits without being able to do anything else.
The problem with positively defining intelligence is that all such definitions seem to end up begging the question and are therefore unsatisfactory to somebody. Which is what makes the Turing test philosophically interesting.
I don't know about limits, you can decide for yourself what it would take for you to be convinced some agent is "intelligent." The fact that we've been trying for 70 years is completely immaterial. How long until we got the ability to fly? Seems like we had been trying at least a few thousand years, that says little about feasibility.
The test is an adversarial game, and both sides can attempt new strategies of fooling or seeing through the opponent. I think your claim about being able to pass any set of limits is rather bold, and I would be curious about arguments for it.
We're already in the territory where there are certain applications for these chatbots, and there is no fundamental argument why we this line of research could not progress further until it reaches its goals. I don't mean to say I believe we'll have AI soon, just that you can't fault the Turing test for not doing what it should.
What do you mean when you say there is a problem with positively defining intelligence? Do you think we should define it negatively? There is a lot of criticism of the Turing test, but alternative proposals are exceedingly rare.
While the limits in this case were admittedly rather strong, this does not form a fundamental objection to the test. The bar can be set progressively higher.