Update 19/08/2015 I just recently found the thought-experiment tag which is identical to the one I was discouraged from in my proposal below. Did something change in the arguments?
I would like to bring this issue to your attention and it would be very nice to know other position and comments on this, I think something useful can come out of this.
Motivation: After reading many questions and comments I have seen that several questions are oriented to better understanding the principles and corollaries of a theory.
The problem I see is that they receive lots of comments which point out irrelevant observations, I mean in relation to real purpose of the question.
Specifically, comments adding information from other areas of physics, or pointing out the infeasibility of the experiment. Nevertheless, when discussing about a certain theory, pointing a paradox or drawing conclusion from it, even if the scenario proposed includes other phenomena not explained by this theory, the relevant discussion might not always need the detailed knowledge of those phenomena which might render this scenario impossible, and the question still be a very valid one.
Example: Let us think about Einstein's famous gedanken, or thought experiment, of the relativistic train and the 2 observers.
This question is aimed to better understand consequences the theory of relativity and is completely valid. Comments or answers focusing on how the mechanisms for switching light on would work, or how the persons can not see something passing at these speeds, etc., all are arguably valid but out of scope in this case.
Here the point is, assuming all conditions imposed in the scenario, and not contained in the theory, hold: how do the we explain/understand the consequences and their relation to the theory postulates?
Conclusion: Using this tag would have the benefits of:
clarify the type of answer desired: this separates questions wanting details, numbers, technicalities, from those exploring underlying principles, or reflecting misunderstandings of a theory.
preventing out of scope comments and answers: the people will only contribute with posts of relevant aspects, when they have a clear idea of what they are talking about and not bring to attention their knowledge on tangential-to-question subjects.