Weird nitpick, I know.
There's also a slew of drones that may or may not use efficient small piston engines or rotary varients which may or may not count as piston.
On the data aquisition side I'm willing to bet there's still a place in the US military for low, slow, ground hugging piston engine craft that run radiometrics or EM mapping.
https://en.wikipedia.org/wiki/L3Harris_OA-1K_Sky_Warden
It looks like someone is abusing a small prop plane that's normally used for crop dustin and just duct taping some cheap weapons to it.
Because that's exactly what it is
I'm getting strong PAC 750XL family vibes from that, we had a modified version hardened to fly 80 m drapes across all of Mali some years back .. locals were taking random potshots as it passed over: https://www.youtube.com/watch?v=1_MO5Wfomks
Our civilian aerospace industry had a scandal a decade or two back because apparently various African countries were buying our trainers, discovering that as shipped the trim was a little off, and rebalancing by mounting MGs in the too-light-because-it-was-empty space.
Crop dusters carry weight, excel at STOL (Short Takeoff and Landing) on "Oh shit, that's not a runway".
US Special Operations Command is into the sneaky stuff - intelligence gathering, quick in | out person on ground infil and exfiltrates.
Stubby little planes that pull like tractors and can depart flying upside down underneath a bridge are ideal, they get overshot by fighter jets and have engines too cold for air to air missiles (fingers crossed).
I'm guessing that these days there are two kinds of airborne objects: multi-modal drones and targets.
Oddly enough, heat seeking air to air came in ca.1950s, so self-flying has been around a while, and now people (especially those with heavy logistics requirements) are talking about land based self-driving, but shouldn't the seas be an intermediate problem? Where did all the self-sailing vessels go?
Also Boeing was developing the F-32 (which lost out to the F-35) in the mid 90's, so it's conceivable that an engineer on that program might still be around in some role.