This thread got picked up on another woodworking forum, and I glanced through it.
The single curvature mold is probably better than the conical one, there really isn't any reason to build a conical arch into the soundboard, because the wood is already stiff in that direction, and therefore deforming it, is making a lot of weird things happen. You are building a pre-stressed structure in the direction of the stings, and then throwing an s curve into it such that the deformation in the direction of the soundhole (what we seek to avoid), is actually releasing the pre-stress.
(Pre-stress is above my pay grade, but it is the weird world where bicycle wheels support their weight on columns of the spokes between the ground and the axle, contrary to the perception that they hang from the spokes.)
The transverse curve is traditional and does not do bad things to the wood given that it flexes easily in that direction, and it stiffens the board in the same direction as string pull. Some nylon string guitar theory is based on the idea that a relaxed soundboard is a good soundboard.
Uber jig master, and teacher to the many, Charles Fox, has recommended this style, or uses it.
The only downside is that it makes the guitar look a little funny; you can see the curve a little since the fact it runs transverse only, leaves the rim of the guitar at different heights. It is subtle but if it isn't something folks are clamouring for, so it isn't going to help sales.
There are a variety of reasons why spherical molds are used:
1) Once you tool up it is actually easier to build this way, and everyone seems to be tooling up;
2) It has a strong chance, as also with the OP/Fox method of reducing board splitting due to misuse, or too much travel.
3) The bridge dive thing; one way of addressing that.
4) I has virtually become mandatory in custom type instrument builds.
Someone mentioned it is traditional which it is not, depending on your time horizon.
Ukes on the other hand:
1) Use some tough woods that are heavier and thicker than guitar woods
2) Light string tension
3) Hawaii doesn't seem to be splitting, how is it working out in world trade?
4) Top are tiny, which also reduces splitting.
I turn my workboards on a lathe, which takes a pretty big lathe for a guitar, but for a uke, not really. I use spherical boards, because everyone else does, though I use as little as possible.