The ADE version will be, as mentioned earlier, is a means for Microsoft to test the waters for a digital only console without re-tooling the factories.
The next family of Xbox hardware is being developed and it would be a waste of resources to re-design the current gen just for an all digital version.
I wonder what they are learning though, PC has been all digital for years, having Windows 10 sucking up our data and their own store they should know plenty by now.
I think the biggest barrier is internet speed and game/patch sizes.
Our new build development only had fibre available a few months ago, I signed up immediately, was an absolute nightmare having a 3mb connection, took days to download anything substantial.
The next Xbox may have a digital version in addition as an option but there is no way they'll ditch optical drives globally in the coming generation, there is too much patchy/slow coverage to make it mandatory. If they do they'll lose even more market share to Sony.
They also need to sort out the pricing of new digital releases, no way should thrt still be costing more than retail. I get all the reasons why this is but needs to change, sorry if GAME goes out of business but times change.