I guess if you're trying to squeeze every possible penny out of a set of brake pads and you are OK with running them down to the "chirpers" … then it doesn't make any sense to change them early. The caliper pistons will probably be OK after sticking out to the limit and being exposed to the elements. Doesn't matter if you're on a long trip when they do fail, you can just stay overnight somewhere and have it done and you will have saved a few bucks by running them to failure. Hopefully they wont fail on a long hill. And while you're at it … no need to change rotors unless you start to feel vibration , hear noise , or have some other problem. No need to change rotors at the same time you put in new pads … they will eventually bed in and you can just live with diminished braking until that happens. Also, buy the absolute cheapest parts you can find with no concern for any notion of quality , performance , life , dust , rust , or anything other than cost. The more expensive parts are exactly the same , simply cost more. You can easily clean your expensive wheels frequently and the brake dust wont damage them.
In fact, some pads with good life left on them can be obtained from a junkyard!
I know you are mostly being facetious but I don't buy the absolute cheapest rotors and pads. I buy quite adequate ones.
I buy Brake Best or even Brake Best Select sometimes and I used to use a lot of Wearever Silver series. Not the cheapest ones on ebay I can find.
Lifetime warranty and never had any problems or what I would feel is short life and never any performance or operational inadequacies.
BTW, you will find lots of shop mechanics that push the always change or turn rotors or if you replace one side rotor you have to do both....BUT that is almost completely playing the "fear" card because "It's your brakes" you know.
If a car has no vibrations or grooves in rotors there it is completely fine to put a new set of pads to replace the worn down set and the car will still stop just fine and safe and within any safety parameters if was designed to.
Back to rear pads. There is 100% no safety reason to do the rears at same time as fronts UNLESS they have the dame amount or wear. That is the ONLY way you can make a case for anything other than convenience.
In most cases if the fronts were down to let's say 30% pad left, the rears would still be at 60-70, maybe 80%. Zero reason to replace them just because you are doing front.
Caliper pistons have a boot to cover the pistons so sticking out is not really an issue near as much as caliper boots and hardware (pins and boots) being in good condition and greased and free to move.
As a matter of fact it is worse to a piston to be in the same relative position all the time. It can even start to seep and if when you put new pads on and push them in the area there is better and less worn or rusty and no seepage at all.
I guess some put new calipers and hoses on with every brake job. Real waste unless you vehicle is not a standard passenger vehicle used for standard use which is very low duty.
Certain applications merit going through things on a more regular basis not only by miles or wear...but not 95th percentile of vehicle and especially SUV grocery getters.