I'm sympathetic to the idea of fixing gender-specific pronouns, and I agree with your comment that this mode of address may act in subtle/subconscious exclusionary ways. At any rate, English seems to be moving away from the idea that an assumption of 'he' is gender non-specific, and writing style guides are endorsing 'they' as a singular alternative, so one could argue for the more modern form anyway.
However, there's a balance to be struck. We could end up with enthusiastic editors changing this wording on its own, which would push a lot of old content to the front page, reducing the sites' usefulness and annoying everyone. By all means, if you see other things wrong with a post (all upper/lower-case, excessive emboldening/italics, lack of paragraphing, poor spelling, txtspk) then you could change this at the same time if you wish.
Just be aware that, whilst most people won't mind, some people will strenuously object, and their counter-reaction may result in damage to the original cause. Thus, it is probably wise to tread carefully. Unfortunately, gender equality and the principles of political correctness are politically polarised, and we cannot require people to endorse them prior to using the site.
I will occasionally edit out instances of 'lame' (i.e. disabled) and 'retarded' (i.e. learning difficulties, see here) for much the same reasons, but I don't go on edit hunts. That seems to strike the right balance, between shaping Stack Overflow to be welcoming place for everyone whilst not censoring every lazy use of inappropriate language.