Not 100%, but pretty damn close to 100% sure you can't. How you might be wondering? Watch every video that has a downed player in it and you'll never, not even once, move an inch from the stop where they were downed. So i would say that is my main thing.
Future Content refers to that which may be added later, of which we know almost nothing at this point.
If you'll note from the original comment of mine that you quoted, I am not talking about being able to crawl while incapacitated, I am talking about an ability that will allow the medic (or as Rev suggested, anybody) to drag an incapacitated player out of firing lines.
I am aware of what is currently known to be in and what is currently known to be out, but since there's only so much that can be done with the information, many of us are choosing to discuss how certain added mechanics could work and if they would be interesting additions or not. Sure it's not likely to be an addition based on current in game mechanics, but it doesn't mean we can't talk about it.
It is, after all, a discussion forum and it can be quite boring if nobody is discussing anything.
And I should note that a portion of that in my last comment was directed at the "/end topic", as I see that far too often when there is still plenty of healthy, safe, uninflamed discussion to be had.