Looking at the new Transporter from a campervan conversion viewpoint, as it is based on the Ford T-Custom body, it will presumably have the same advantages and challenges.
First, although I detest electronic handbrakes, and won't personally ever buy a car (or van) with one, there's no doubt that swivelling the front seats should be considerably easier in conversions with this feature.
Secondly, the new van will be slightly wider than the T6.1 (1.95m as against 1.90m), and has less tumbledown on the van sides. So, perhaps slightly more interior space to work with - though that's not a given, depending on 'crashability' structures.
On the downside, the extra width makes the van less handy in country lanes and town centres.
The new one should have sliding windows which don't leak - a standard feature on Transporters from T5 onwards, unique to VW. Hooray!
The main difference, though, I think will be the lower roof height of the new Custom/Transporter.
This may be good, as rising-roof campervans should be able to 'limbo' under 2m height barriers more comfortably.
Potentially bad, though for interior seating - on the previous Custom, if you sat under the roof cut-out, there was very little room for your head (a significant amount less than the VW). Factory high-top Customs ended up with only 5ft 10 headroom - nota problem with Transporter conversions.
On this one, with a lower roof, it could be very difficult. Seats would have to be set lower, which might need a re-design by the seat suppliers.
I'll be very interested to see the first campervan examples!
For driving, I always found the Custom much better for fast road-holding and handling than the Transporter, so that may continue.
It's all academic for me though - I'm happy with my T6.1 conversion, and couldn't possibly justify the colossal price of a new campervan, so this one will have to outlast my driving career!