I felt Sherlock WAS about to tell him something important but changed his mind - what it was, though, I don't know.
I tend to view the relationship as a very deep and enduring friendship though (or I did, until this episode) and really don't see any romantic side to it !

It's difficult to make predictions. I tried to do this analysis in an objective way (as far as that's even possible), based only on what is really there in the episodes. Sherlock and John refer to each other as "friends", so I kept that. What you can read between the lines is extremely emotional, although physically almost nothing happens. There are very strong symbols and metaphors like death, romance or sexual things, saving lifes, dying and killing for each other. That could be a way to make it clear that the relationship between the two is really meaningful and passionate. Otherwise it would be "just friends", and that would automatically appear rather insignificant. But I have no idea, of course, what will happen in the future. Could be anything. I like Johnlock in fan fiction and so on. In the series I'd rather see them as friends, although I'd also be okay with actual Johnlock in the series. Or whatever - if Sherlock decides to get married to some girl in the next series, I could probably even get used to that. From what I've seen so far I didn't get the Impression that this would happen, but you never know.