If Apple really intends on selling full movie downloads, then they have two options: make their standard hard drives really, really big, or offer online iDisk storage to all who want to buy a movie. It seems that Apple has gone with the latter. If they are smart, they'll not make this iDisk plan the only option for viewing the movies. Full quality (in some flavor of H.264 HD, 720p or otherwise) downloads should be available to those with the necessary internet bandwidth and local storage capacity. Lower quality, iPod ready downloads should come with the same dual-storage options. If you have the iPod version locally, then you should have access to the HD version online and for download to an external storage medium (DVD or HDD).
The whole content delivery paradigm that we have now with the iTunes Music Store would have to be overhauled. Music works pretty well with a pay-per-download system (allowing the user to keep copies of the song on several local machines and iPods). Moving to a larger file like a movie and you run into storage capacity problems right away. Assume for now that Apple is still going to use the line that "this is all to boost iPod sales". This means iPod versions like the current TV and Music Video content will have to be available and at the forefront. Full versions would only be of interest if Apple comes out with a DVR Mac mini. This new iDisk idea makes the DVR option all the more interesting.
What if instead of simply recording TV content like a TiVo DVR, the mini was you local storage site for all the Movie content you download from Apple. The mini would become the focus of the Movie Store just like the iPod was the focus of the Music Store. Sell more HD movies to boost Mac mini sales!!

The mini would need a much larger hard drive (or two) to make this work, but it is possible. By offering dual-downloads of both HD and iPod sized files Apple would also keep the mini from having to bear the brunt of H.264 encoding for all the movies you choose to download. Click to buy the movie and you instantly* get both formats (*minus the download times). For those without a mini (or a suitable PowerMac with 500GB+ storage) you can always leave your HD content online in you .Mac iDisk and just take the iPod sized file with you.
If all this is tied together with a sweet marketing campaign, flawless software, speedy downloads, and signature Apple hardware, it just might work!