I did some reading about TPMS systems and I can't believe that
1) Subaru doesn't have a 5th sensor programmed to recognize the spare, what if you stupid spare donut starts to go low...you wouln't have long on that thing. At least the Subaru has a spare tire, some other brands don't. The lack of TPMS on the spare is not a significant issue to most of us.
2) Doesn't allow for Snow tires for folks up North, the federal law prevents a tire shop from swapping non TPMS snow tires out for winter, end result is people without cash are pushing their summer tires in winter, endangering everyone. I've done lots of research and while I do find many "internet experts" citing this "federal law", I find no mention of it in the criminal code. In fact, the federal law requires TMPS systems on new production vehicles, but does not require owners to maintain them on snow tires. Show me the law and I'll concede defeat on this one
Found a link for a 3rd party computer that allows TPMS reprogramming at home for 150 bucks at home, but it doesn't sound super straightforward. I do have snows on separate wheels, which I purchased from Discount Tire. Each year they re-flash the sensors to my car at changeover time, no charge, takes 2 minutes
The other annoying thing is I'll need to buy a matching alloy wheel from the dealership for the spare. If you really want to rotate all five, yes, but when was the last time you needed a spare?
Can't believe full size spare with TPMS isn't even an option on cars touted for off road handling. I tend to agree here, with the Outback being marketed for the outdoor folks, a full size matching spare would seem appropriate.