Hi Burr, sorry I'm still not sure if I'm understanding...

> But basically sliding the apex of the buldge around could be useful.

Do you mean a slider to control the bulge like this one here: ?




> And then the flip, I'm not sure how/if that works...I
> understand it's about applying a curvature from the
> existing surfaces, but then to be able to flip/invert that
> could be some type of cavity tool.

You can do this with the current Blend command by entering in a negative value for the bulge, that flips it to the opposite side, here's an example:



- Michael