Besides, who drives stick anymore? I've driven stick since I learned to drive forty years ago, and I even I admit that I can't do better than a computer-controlled DCT, on performance or fuel efficiency. Next car is either electric (we already have a Leaf), or DCT if we must.
This seems like a bad tradeoff. Increasing wear on expensive, hard to replace parts (your engine and transmission), so that you can save on relatively inexpensive, easy to replace parts (your brake pads)
So that's not actually the tradeoff you're making. More to the point you run a much higher risk of acute failure with brakes than with anything else. When that happens on a downgrade you can't stop. If you were actually increasing wear on piston rings (a laughable argument at best) you might end up needing to rebuild the engine after a few decades.
But it could be bad for your piston rings and catalytic converter [2], so there's that...
[1] https://en.wikipedia.org/wiki/Engine_braking#Gasoline_engine...
[2] https://ricksfreeautorepairadvice.com/engine-braking-cause-d...
Oil in your catalytic converter isn't good, but that's why you have one or more spark plugs per cylinder — to burn it. There's the issue of heavy metals in the oil (e.g. zinc – generally in the form of ZDDP) that can damage your cat, sure, but that's why the current API specs have reduced the amount of allowable zinc a revision or so ago (API SN or SM I believe). Zinc is a great anti-wear additive but in high enough concentration can damage your cat.
Stop and go traffic will wear your clutch out (assuming we're talking cars with dry plate clutches here and not a motorcycle or anything else with a wet clutch). Engine braking will not (assuming you're not riding the brakes or constantly shifting while trying to slow down). Hell, even if you are downshifting needlessly if you're rev matching you're not wearing the clutch all that much. I'll take this fictitious clutch wear over acute brake failure thank you very much. In fact I've yet to destroy a cat or clutch in San Francisco traffic.
Uh, no.
And, an educated guess here, probably increased emissions on the overrun.
Also, no. Most cars built in the last 30+ years will stop injecting fuel during overrun.
Plus, it typically only applies to Semis as their engine braking is especially noisy. On a typical gas powered sedan you would be hard pressed to identify that someone is engine braking unless you were right next to it. Being prosecuted for it would be even more exceptional.