Ross,
If you get the k, you'll lose the Svideo output (if you use it at all). Also the k's are based on the same hardware chipset as the new 922's are and if they bring any features down it would be to the k's before any others. I'd also expect the k's to outlive in the product line the normal x22's as this chipset seems to be the now norm and development will slew toward it. But I wouldn't get a K solely based on that. There is no expectation at all that they will support any of the 922 functions in the k series because they want you to upgrade. But, an example of the above is that the new SRS TruSound will be supported on the 722k before any other legacy receiver including the 722.
On the HD failure issue, take a look around for a very long thread on hard drive temperatures in this forum. The VIP's are not very well engineered as to air flow and cooling they run very hot. If you have your unit in any type of enclosure then that will just exasperate the problem.
I have 3 VIP's and all 3 of them have a ThermalTake USB fan cooler sitting against the exhaust area (the left rear side, looking from the front) of all the unit sucking air out.
Amazon.com: Thermaltake Mobile Fan II External USB Cooling Fan - Us: Electronics
All 3 of the VIP's now are actually cool to the touch, have internal HD temps (Menu-6-3-Counters-4 page downs) below 110 deg F. If you've have 2 failures and any of the above I really recommend supplemental cooling.
Also, the EHD option is great if you have have recordings that you simply cannot afford to lose. I have 4 EHD's on my shelf that I just move the USB cable between. Concerts/Music, Movies, TV Shows/Series, Other( Documentaries, Specials, News, etc). If I record a movie that I want to keep (I.E. I just recorded the new Australia premiere on HBO yesterday) I immediately move it to the EHD and then watch it from the EHD when I want.
This way I keep the internal drives as clean as I can and also have the least to lose on a failure. Also, it's nice to have the free space on the drive as the only way you can migrate shows from one EHD to another is to restore to the primary drive and then dump again to the new EHD.