The problem is far more heat/flame exposure to the top ring (that is IF thinning out the crown thickness doesn't do it in in the first place) the top ring is the only 'true' compression ring.. The second ring, is mostly oil control, even though it's called a compression ring. It's why ultra short pistons only have one compression ring and do ok (it's preferable to do that than to narrow the piston crown too much).

It's the sort of thing that might survive in a drag race engine, or MAYBE a circuit racer doing only short sprints, but it's a bad bad bad bad bad idea for anything you want to clock up decent miles on. Top ring life pretty much = engine life (or at least useful engine life) at least if everything else holds together. thinning the piston top that much will accelerate top ring demise. No question of it. Which means it'll be putting contaminants past the rings quicker, and speeding up ring/bore wear.

I'm not suggesting you'll only get 500 miles out of the thing, but it certainly isn't an option where you'd expect normal engine life (i.e. into the hundreds of thousands of km's with proper oil/change/maintenance).

I dunno what options everyone has out there, but I'll put it another way - if I couldn't get a15 pistons, but a14 gear was plentiful, tben I'd simply look at building an a14 instead of a 'compromised' a15