I think TiVo provided a glimpse into the future of Apple TV when it released the TiVo Stream add-on for its 4-tuner DVR.
I'm familiar with it, and it's definitely very cool. I'm already doing something very similar. I have a Windows Media Center PC along with a SiliconDust HD HomeRun Prime (networked box with cablecard slot and 3 tuners). I run Plex's server app on my PC and another script/app which renames my Windows .wtv recordings so that Plex knows how to pull down the metadata for them. Then, I can run the Plex client app on my iPhone or iPad and stream my recordings to those devices, including then pushing them to the ATV via AirPlay.
One big limitation is that I can't watch Live TV on my devices. The Plex server app can only deal with .wtv files that have finished recording. Also, in order to get high picture quality, you need the computer running the Plex server app needs to be fairly current/powerful. TiVo gets around that latter issue presumably by having some sort of hardware-based MPEG2-to-MP4 (or whatever) video encoding chip in the TiVo Stream.
The other solution that Apple could go with (which I've posted about before) is to create a Windows Media Center alternative. El Gato makes EyeTV which is along those lines, but their software doesn't support cablecards, so you can't tune in the full cable lineup. Apple would need to develop the DVR software and get it certified by cablelabs. IMO, rather than make it an OSX app, they should create a new AirPort Extreme/TimeCapsule router with a built-in cablecard slot, iTunes server, DVR functionality, and a chip capable of doing MPEG2-to-MP4 on-the-fly transcoding, so that the shows would be recorded OTA or from the cable company, converted on-the-fly to MP4, and stored on a hard drive. The on-board iTunes server could then serve it up to all of your iOS devices in your house.
But I suspect that Apple (Jobs?) didn't like that approach because it still saddled the user with commercials (they could have software designed to strip those out, but those approaches aren't always foolproof and it would also put them in a bad relationship with the cable companies). So, instead, their approach has been to try to establish relationships with the content producers, and offer a-la-carte pricing for shows. The other advantage with their approach is that the shows are stored in the cloud, so you can use whatever router you want and don't have to worry about how much free disk space you've got.
I have no problem with their approach vs the one I've thrown out their as an alternative, but the main problem with it is: a) they haven't seemed to get the per-show pricing as low as most consumers would want to see it, and b) there's still a need for live TV (e.g., morning news, sporting events) which they're present solution has yet to fully address (e.g., there is an MLB app, but no NFL app).