I think they will include a DVD drive for backwards compatibility, maybe even a BluRay drive to allow the system to be an entertainment hub.
However I think the next generation of software will release on digital distribution PLUS cartridge/memory stick media.
My reason for this is two fold. Firstly, cartridges allow for the release of a cheaper console with, no mass storage device, just flash based memory for saves and firmware only, the game can run off the cart directly. They may even go for an Arcade model that has no optical drive to reduce costs further and backwards compatibility will only be offered in the Pro/Elite. Perhaps an Elite would have BluRay.
Secondly it means that they won't limit their markets to countries/customers with massive internet connections that can download 10-50GB games on a regular basis.
Proprietory optical media wouldn't be a terrible idea, even HDDVD, but I think new gen games are going to need more than just massive data storage, the quick access of ROM or HDD will be much more important.
I certainly hope that's the case anyway. Whoever goes down this route will be far more likely to get my money. I certainly expect Nintendo to return back to carts for their next generation. It will most likely be more cost effective for them as they won't demand as much storage space for the games as the PS4/720.
Never argue with idiots
They bring you down to their level and then beat you with experience
