I believe "Magento 2" term in the title makes more sense (right now). Because most of the questions which are asking here is about Magento 1 and Magento 2 is not using in production level. So most of the questions that is related to Magento 2 is asking by people who are more engaged with Magento (ie developers only, not merchants or any other cateogory of people).
"Magento 2" in the title immediately makes sense to every one who love to learn more about Magento 2. For others, those questions can be easily neglected. Yes, question count is increasing, I agree. But still it is "too less" compare with Magetno 1 questions that are asking in a week. So tagging "Magento2" in title will immediately make an attention and I think that is good way to go now.
We need to think about this later. After magento 2 become stable or at-least questions related to Magento2 is comparably large with questions related to Magento1.
What I am saying is, it is not a big deal. If you look for such questions in @stackOverflow, you can find lot of examples of such questions. For an example, if you look for
laravel questions, there are lot of questions which have a title that holds version in it. There are questions which specify version as a tag (which I prefer, of course) and not in title. In my normal observation, community members over there are not trying to "filter" them REGULARLY.
Also specifying version in title has an extra advantage. When I search in google something like "Namespaces in Magento 2", we can see that, Google provides more importance to the title rather than tags. That means question with title which has a term "magento 2" within it will come first in search. I think that is a good thing, right ?
Also after we graduated, people who will have priviledge to edit the questions directly is going to reduce drastically and hence filtering such questions will become more difficult.
So my advice is, let us leave this to the OP. If he needs version in title, then allow that. But if we have time to filter such questions, then there is no problem to edit and put the version as a tag. :)