It's been officially announced, and is essentially the premium passes for DL and WDW together - for $700.

They go on sale starting tomorrow at both DL and WDW.

If you have a premium pass at both you're already upgraded, and if you own one AP, you can upgrade for the difference.

I might give this a try as my WDW AP expires in December, and would be an interesting test. I'm hoping for a DVC discount, but haven't seen anything about it yet.

Full details here:
?Disney Premier Passport? Unveiled Disney Parks Blog