If anyone has read the HRM "Speed Demon" article, the piston shown is a bit of a puzzle (and the auto shop quality of the author leaves much to be desired).
The LS is, obviously a quench chamber with tilted valves, and a chamber shape & volume designed to keep the CR in line with high boost.
However: the dome is a bowl with a round island centered in it. In a valve face this is what DV called "penny on a stick". I think the island is not a compression bump that doesn't interfere with overlap flow, but something else. It may be relevant to Trick Flow etc. heads.

Picture here: https://hotrodenginetech.com/speed-demons-ablown-fuel-streamliner-motor

Before I make a guess, any ideas?

I'm going to guess here but I'm thinking that's a mixture motion piston top (my limited education stops me from giving a better description) to induce a more homogeneous mixture. Or maybe it helps suppress detonation in some way. At 60 pounds of boost for that time frame I'm sure that detonation is an enemy.

The thing that stuck out more than that to me, was the fact he was using a gapless top ring. Some would say the engine builder is stupid for that, because they don't work.

Just weird things you see sometimes.

Cummins diesel engines use that piston design because the injector spray holes are right above it. Helps distribute the fuel across the cylinder before burn.

Thanks, that was sort of where I was going. A little circular running path for mixture to swirl instead of just being pushed down?
Many smart people have said "the piston dome is the bottom of the combustion chamber", I just have this gut feeling that what we accept as choices now (dome, wedge, flat, dish) is shorter than the possible list, but what are they? This may be one for chambers resembling the LS.

Maybe the heads are set up for direct injection? GM has been experimenting with that for years. Still haven't been able to get past the "gumming" issue. But getting closer. I think FCA is now producing several direct injection motors. What better place would there be to put the fuel than right down the middle?

What I can't tell from the photos: is the OD of the trough also the outer edge of a circle outlining the LS chamber, and its ID determined by the edge of the intake valve? This would accept charge directly from the opening valve on O/L and give it both a place to go (less shrouding) and a direction. DV is very specific that if the intake flow isn't initiated ASAP there is no way to "catch up" by delayed intake closing.
Not being able to analyze what's going on here in the B&ATDC O/L time period is very frustrating, I'm try to design a piston dome for a very weird chamber.

Cummins diesel engines have no chamber. Valve faces sit up just slightly higher than deck surface. So I would say that the OD of the trough/chamber is relative to the outer distance of the valves. I don't remember, but pretty sure that the exhaust valve isn't much smaller than the intake, if any smaller at all. 4 valves per cylinder, too.

My first thought was it was the direct injection liked the thing in the piston as they do have funky shaped pistons but that engine has all 3 injectors in the port so I would say it has to do with spinning the mix around as it comes in the chamber,

Probably helps with strength as well. The circular part in the center is right over the void on the under side. 60 psi is a crazy amount of boost.

Many "dome" pistons really kill any charge motion in the cylinder as the piston approaches TDC. As it was mentioned, the piston crown has to be treated like the floor of the chamber.

This engine is not DI, and DI piston crown features are only present for catalyst light off, to keep a rich pocket of fuel at the spark plug. Pistons in central mounted DI injector engines will look similar, albeit less exaggerated, as they want to maintain some quench along the outside of the chamber, and you have to build up material in the center to gain back CR, but not so much as to "cut" the chamber in half at TDC.