I was under the impression the DE had a new sound mix. If that's the case, then seamless branching would be a bit harder to do.
(Having said that, I hope that all three versions are eventually available on the same Blu-Ray disc at some point, similar to the Alien and Blade Runner discs with multiple versions out there).
The DE does have a new sound mix and yes it wouldn't be feasible to have it with the other two versions.
I meant to say that the Theatrical and the SLV could have been put together on one Blu-ray and the DE could be separate on another.
But they failed to that and now it's unlikely IMO we'll ever see the SLV on Blu-ray--for those who prefer that version.