Jon,
As I mentioned previously, a piston type you refer to has been used, but primarly in engines with very little combustion chamber volume iin the head itself, such as the Jaguar V12 HE "Fireball head". It essentially reverses the position of the combustion chamber shape into the piston crown, instead of in the head.
In practice, a hemi does basically what I think you are intending to achieve, but does it in a "half-sphere" which is what a hemi-chamber is.
And, it suffers from the conditions which are present in a hemi-chamber, and which also would cause issues with hi-compression in the "sphere" design you describe, because of the lack of "squish/quench" area, which results in detonation at high compressions. In fact, one of the main reasons why our engine is compression-limited is because there's no quench area in the chamber, so anything higher than about 8.5:1 compression results in detonation from lack of chamber swirl, unless fuel modifcations are present, such as octane boosters or the like. Whereas, if we had a piston that offered good quench area, we could probably run 10.5:1 on hi-test pump gas without detonation. But, nobody is making such a piston for us, so that's that.
Regarding the long rod, it's a geometrical issue involving thrust angles. And it does affect dwell time as well as MBT angle, and affects the overall stroke behavior in all strokes, including changing the flow curves for breathng. And a long rod weighs more.
In the case of the Bullet, we have a long stroke and a long rod and a long piston.
It's LOOOOOOOOOONG in all kinds of ways.
I think it's great that you're interested in this stuff.
I'd recommend doing some basic research into the most basic and even boring aspects of engine design theory, so that you start with a full understanding of what things do, and how they can be manipulated for different results.
The "golden rule" of modding is "Just because it worked in different application, does not necessarily mean it's going to work in my application". So always look at everything in total, and how it all works together, and crunch the numbers to see what's what in YOUR application. Some of the most basic and earliest design decisions that you make, can actually "cast in concrete" how much power your engine will eventually be able to produce.
An excellent example of this could be made with some of the stuff I wrote on this thread.
Let's say that you heard from Harry Hot Shoe, who races NHRA dragsters, that huge ports are the best way to make power, and open them up as big as you can for better breathing. So, you grind open the Bulet ports to 34mm or even bigger, and use a 1.5" Amal GP carb to feed huge air volumes in.
Then you read my thread here on late iintake valve closing timing, and think "Hey! That's the ticket! I want that too!" And so then you re-phase your cams, and the engine doesn't respond as expected, and in fact gets worse.
Well, big slow ports and late IVC timing are not terribly compatible, and they work against each other in most applications, so you pick which approach you are going to go for YOUR application. You don't necessarily try to "get both", because "both" may not work..
So, virtually nothing actually "stands alone" in an engine design. It all depends on the way the rest of the engine is designed and working, to make any mod work properly.
There's alot of engines out there that have been modded poorly, and are actually worse than stock.