I would guess 1,4,5. Certainly, there is no 'LaTeX-by-default' policy. So #6 is out.
It's worth thinking for a minute about who is the target audience for tex.sx. Maybe this is worth a question of its own, but let me outline my thoughts.
The real hard-core TeX users (of whatever variant), already know how to find stuff and are on all the mailing lists. The slightly savvy ones are similarly fairly used to finding out information via CTAN or search engines or whatever. Also, more computer-wise users don't shy away from joining mailing lists and so forth, and there are plenty of those on TeX and friends.
But there are loads of people out there who use TeX and friends in their jobs, but not as the front-line component. So they come up against stuff now and then, but not often enough to warrant joining a mailing list and wading through all the other 1000 questions. So they find a hack, they pad their document with ~s to get the spacing right, and though they know it isn't right, it's not important enough to spend a long time trying to work out the right way to do it.
Those are the people that tex.sx should be aiming at because of the low barrier-to-entry of tex.sx, and the fact that people can "come for the answer, stay for the questions". You don't have to wade through everyone else's questions, or length discussions on the merits or otherwise of LaTeX versus ConTeXt. The SE engine is perfect for this lot.
But to most of them, TeX is LaTeX. So we assume "latex by default" simply because that's the assumption of most people coming in. And they don't want to be browbeaten with people insisting that they Get It Right. But if someone comes along and says, "I know you asked about LaTeX, but here's how you would do it in ConTeXt" then after seeing that a few times, they might think, "Hmm, maybe there's something in that ConTeXt stuff.".
So don't stress about the number of ConTeXt answers. If you want to promote ConTeXt, go ahead and add ConTeXt answers everywhere. So long as you don't come over too heavy, no-one's going to vote you down (at least, they shouldn't). I do that with TikZ: even if the question says "xymatrix", I'll put up a TikZ solution. Sometimes the person says, "Thanks, but no thanks" but sometimes they say, "Hey, that looks great. I've always wondered what the fuss about TikZ was about, now I can see a reason to look at it.".
One of my reasons for spending time on MathOverflow is recruitment. Not particularly of graduate students, but of ideas. I try to get my ideas out wherever I can, so that more people are aware of them and more people are thinking about them. I look for places where I can say, "You think you mean to ask about X, but actually if you think about it like this, then you'll see that you're really interested in Y.". So long as it's done politely, there's no harm in it.
So see the lack of ConTeXt questions on tex.sx as an advertisers dream. You get to pitch ConTeXt to the rest of us and show us why we should switch.
(Just realised I wrote "you" a lot, but the question was asked by Caramdir who confesses ignorance. The "you" is really the ConTeXt crowd.)
