I suggest Wizards does not build a single series of linked adventure modules to showcase their additional rules. Doing so would contradict the whole idea of modules in the first place: their optional status. Individual adventure modules however, should do just that. Adventure content that showcases the latest and greatest is definitely needed the day the optional rules mods come out.
My desire is that Wizards goes shopping for big name talent capable of delivering. That costs money, but they have it. I also believe they should utilize another huge asset for them: copyright. They own A LOT of copyrights and piecemeal adventures could sell well to particular groups that already have a following. Designing adventures and then demonstrating how those adventures could conform to previous copyrights for the adventure would also help. There are also copyrights that in the past have halted their original creators from publishing for their own creative work.
Cases in point:
- Castle Greyhawk and Gygax's last great project. (they should definitely go after this for 5th)
- Maure Castle (Kuntz never did finish his extremely popular work here)
- Later Gygax work like his Necropolis adventure for Dangerous Journeys
On top of those they could republish iconic adventures from the early years with the new rules in place.
And, oh yeah, they also own Avalon Hill, a brand ripe with solid games, game rules, and perhaps even supportable products.
So rather than an adventure path, I hope they: look at what is already selling and who the designers are, then pinpoint particular works for sale rather than going for a subscriber-based adventure model. If connectivity is desired, include a section on how each adventure can fit in any campaign setting using the published settings as examples.
side point ----> Ironically the Planescape setting was antithetical to D&D for the first decade or so. However, planar travel within the prime material worlds, dimensions, and inner planes was pretty commonplace. (You just didn't get to play in heaven or hell for numerous reasons) By the mid-80s dimension hopping was tying every game one could think of together to sell Uber-Game Systems.