My guess is that the 500 series machine changes will be mostly cosmetic, if you look at the Bernina 8 Series and the 3 series, they look very different from the Artista/Aurora lines. I'd stake my life on it that they will not include dual feed or the large throat of the 8 series, otherwise there would be no market for the 820.
As for the difference between the 440 and the 630, I love them both. The 440 has push buttons, some folks love that and some hate it, whereas the 630 stitch menu is on screen entirely. Of course there are more stitches on the 630, and more flexibility in personalized options.
They both embroider beautifully, but the 440 (and 430/450) require a computer to be tethered to it, with the computer operating the embroidery. I HATED this feature. That's the only reason I would recommend the 630 over it if you want to embroider.
When the 500 series is released, you should see some nice discounts on remaining 430/440/450) machine left in dealer stock... once they're gone they're gone.
You do not want the 820 in your RV, trust me. It is HUGE... and ungodly heavy. I can't take my 830 up and down the stairs on my own.