What is the significance of the post-credits scene in Pontypool?

I will not give you the full answer, but simply show you the way to get there:

An interview with the film's director: http://twitchfilm.com/2009/03/from-pontypool-to-the-metaverse-in-90-minutes-a-conversation-with-bruce-mcd.html

Wherein, he says:

That used to be end of the movie, but before the credits. And people thought, what? What? Too much confusion. There is a tradition now where you have something at the end of the credits where you have an outtake, or hint of a sequel. The existence for it is sort of buried in there, well the title of the book sort of suggests it, Pontypool Changes Everything, and one of the things I’ve always love about the notion of this, is that the virus could effect something as abstract as the English language, it can leap into reality itself. Change the fabric of how reality is perceived.

So if you want the full answer, go read the trilogy of books. Everything will be explained.

There is no connection. It is a complete non-sequiter. It makes zero sense. That's the point. Get it?

It's supposed to inoculate the viewer against any possible memetic infection they got from watching the film.

My theory is it's a direct epilogue.

Assuming the virus is widespread or at least still a threat, Sydney and Grant survive in what could be called "the language apocalypse" by maintaining a kind of improvisational roleplay. This allows them to express ideas in a freeflow that inhibits deeper understanding and prevents them from infecting each other.

However, the efficacy of this roleplay is limited, as show in the shift from black and white to color (fantasy to reality; safety to danger). The fake conversation bleeds into a real one the longer it stays on topic ("let's get out of here" is on topic but followed by abstract, noir-ish improvisation... until it gains too much context, becomes "understandable" and dangerous?), represented by color bleeding into the scene.

That conversation itself is a threat by being coherent, but could be precipitated by a realization that they're in an infected zone where roleplay won't cut it. Or it could be playful banter about getting the cheque and going home that gets too real and ends up compromising them.

Either way, the scene congeals into understandable communication and ends with the big taboo: a term of endearment uttered twice ("baby--" "shhh!!"). The film established several times that terms of endearment are carriers for the virus. Grant slips up saying it once and by now we're in full color. When Sydney says it he shushes her. This tells me the virus is still a present threat. Hence the roleplay.

since the disease is spread through the english language ,and understanding it, would make sense for them to 'get out of here' by going to a different country (suggested somewhere in asia with her outfit) where they couldnt understand what is being said around them. idk - but it could stop them from being accidentally infected by people around them, and since he stops her from using terms of endearment at the very end maybe like other horror films there are rules to this one and since they know them theyre fine just an idea

I feel that the concept of it's not the word or eords but the meaning of them is carried on by us trying to figure out what's what. I.E. discussing what it is. They mentioned not to speak rhetorically?, and lots of stuff said on Valentine's day is spoken just to evoke a feeling. As is the way we speak to children, another thing they said to avoid. So lots of things we say to discuss the movie could fall in line with the ethos of the movie