The 'Brief Encounter' bit in in Ep 8 I'm guessing was written by Fay and/or Ori? (nope - see UPDATE below.) I'm ashamed to say I completely missed the reference, never having seen the film, and was wondering why Caroline suddenly started spouting rather melodramatic lines that didn't seem to fit with the rest of it. D'oh!
Current rumour is that the DVD of series 2 will be out in September/October*. Episode 9 (actually a feature-length episode, which should provide a spot of closure for the whole enchilada) should be going out around christmas time. I'm guessing it will come out on a separate DVD, maybe sometime around March/April next year? Last bit just a guess.
No current plans for a series 3. Partly because of the difficulty of getting all those actors back for the same period of time, and partly because the nature of GW gives it a limited lifespan anyway. Series 2 was much plottier than 1, for example, and the exaggerated plotlines means there's only so much further you can go before descending into bathos. Don't rule out any combination of crew/cast working together on other projects though - who knows what the future will bring?**
* Although I've got this sort of thing very wrong before.
** Prophets, soothsayers, and Doctors Who, I suppose, thinking about it.
UPDATE: in comments below rob said...
The Brief Encounter reference was mine, and was a somewhat controversial inclusion. Victoria was dead set against Tamsin having any hint of a clipped Celia Johnson accent, with the result that you now have to know the film extremely well to spot what's going on. Despite the associated visuals, which a lot of people recognise straight away, the melodramatic words are not enough to make the connection. So I agree with you, it ends up sounding rather bizarre.
It should be clear that Caroline isn't talking directly to Guy, but musing out loud, as a wry acknowledgement of the parallels she sees between her love triangle being played out on a steamy platform and the scene in Brief Encounter (of which she's likely to be a fan, given her fondness for trains and romance).
A touch of accent would have put that line into inverted commas, and suddenly even those who'd never heard of Brief Encounter might at least have worked out what she was doing.
On the other hand, it must have been very satisfying for the first person to spot it. Perhaps there could be an award at the convention.
As for the significance of the words in the long run....
... well, we'll just have to wait 7 months to find out, won't we?