I would think that the Manchester base (it already exists for CC) will go to the 744 within the next year or so. It was proposed to add MAN-BGI from the beginning of this year's schedule, but that was postponed. When it will start, I don't know, but I'd guess it won't be too long. I reckon the company would let that shake down for a year or more before any further routes were added. The Manchester market has been very seasonal, which doesn't really fit the company's operation, so I think they'll need hard evidence that Northerners will holiday out of season (and will pay Virgin prices) before they commit big time!
It took long enough for Virgin to be persuaded that there was a business market out of Gatwick, and, immediately after 9/11, Virgin's business traffic retreated to Heathrow (for obvious and good reasons). The suits are not entirely convinced that there are not dragons outside the M25, so they will take their time!