I think that:
1: Martin is rude during interviews fairly often. He’s a sassy little bastard (although both interviewers and fans who’ve met him seem to think he’s funny and delightful, so I assume that he typically stays on the right side of the line between hilarious rudeness and actual nastiness), and furthermore I think it’s his way of managing his celebrity. It gives him the breathing room to draw lines of expectation for fans and the media. And personally, I don’t mind. I think it’s wrong of us to expect smiles and sweetness from celebrities all the time. Their job is not to be nice, upstanding heroes for us. Their job is just to do their job.
2: Of all the cast and crew, Martin is the one who most commonly frames Sherlock and John’s relationship in terms that could be considered romantic. Which doesn’t necessarily mean he thinks it is, but at the least he recognizes there’s something there that rings in a similar frequency.
3: I don’t think we should skip over the sheer level of annoyance the cast and crew are developing over simply hearing about it all the time. They don’t need to be opposed to the idea of it actually happening on the show to be fed up with it being 50% of the questions they get about the show. Which I think is also fair. I get tired of hearing about things when I’ve had them repeated to me way fewer times than these guys have heard about johnlock at this point.
I think that people fail to sufficiently imagine what it has to be like, when they’re doing panels and things before crowds of hundreds of people, and every single time, the single most popular question is about Sherlock/John. And then they’ve gotten attacked with stuff like Caitlin Moran’s tacky reading and things, which honestly is pretty invasive. I’ve seen people argue that actors should be able to separate themselves from the characters, but consider how much exposure to porn containing a character modeled after your personal physical appearance you’d need to read before you decided you’d really rather go find something else to do. I’m pretty sure that if you’re picking up hesitant or recalcitrant vibes, the sheer level of “I don’t want this in my face today, could we talk about something else?” is probably enough to do it.
4: I think it’s important for us to remember that everything we think we know about these actors and creators, we know primarily through the filter of the media. Everything we’ve learned about interpreting the show—how the camera controls the story, how we don’t even notice what we don’t see, all the tricks that can be played by doing something as simple as reframing context—all of those can be used by the news media too. And they are used by the news media. But it’s more insidious, because a fiction show is supposed to play those tricks, but the news media—we tell ourselves—is supposed to be telling it like it is.
Except a lot of the news media, especiallly entertainment news, sees their job as getting attention, not telling the truth.
So when you pick up a ‘feeling’ off the actors, you need to remember that you’re not the only person controlling your interpretation of the situation.
Which is to say, we’re generally probably better off not trying to tell ourselves that we know what they think about anything.
5: The bottom line is, Martin and Ben are both excellent actors, and if the show were to call for it, I’m sure they’d act through a romantic relationship between Sherlock and John with the same skill and professionalism they bring to all their work.