There are set top boxes that have many tuners. The STB uses the extra tuners to anticipate a channel change and tune ahead to the next channel. (Fast Channel switch).

For sattelite tv you wouls need to handle over a Gigabit mpeg-2. Not easy.

Caching without decoding would still be a nice boost, wouldn't it ?

Coupled with a decoder that can manage double the actual frame rate, it should cut the switch time with something like on average 1/4, worst case better than 1/2.

You'd still need the additional tuner(s) to provide the data to cache.