I think a cooler solution without so much redundant hardware (all those motherboards/video decoders/CPUs, etc.) would be some sort of modular tuner design where you can just drop in more as needed as previously mentioned. The only downsides:
- The Ubertivo itself that acccepts all the tuners would probably be expensive and bulky. You can already get a Series2 DT DVR for free with service.
- By having multiple DVRs, TiVo can charge you service multiple times. Charging per tuner in a single box would be lame given each tuner is still using the same source of data and only one DVR's OS to maintain.