I was thinking about this the other day. Full disclosure, it's likely a dumb idea and I'll never attempt it.
Assuming it would be possible to make a clear and bubble-free roto-cast of a mold form.....if one were to use a high-temperature clear epoxy with a thick enough wall, could one make a lava globe into whatever shape they desire?
Obviously, I'm assuming there'd be multiple challenges to this from the pressure difference created by heating the wax, getting thick enough walls to withstand the pressure, thermal stress over time (even though it's high-temp epoxy), and concerns with stickage on the inside surface since it's epoxy and not glass.
To say borosilicate blown glass is not cheap is an extreme understatement. Were it possible, high-temp rotocasting could possibly open the door to low-cost low-volume rapid prototyping certain forms for custom lamp globe shapes.
Borosilicate blown glass does offer the ability to do multi volume vessels, allowing forms to pass through walls, and superior durability, quality, and optical clarity.
The rotocast process would mostly require building a rotocaster (which can be done cheap and used repeatedly), designing and fabricating the forms through 3D printing and silicone (though silicone is very expensive), and mounting the mold. The casting material would need careful consideration and likely would require a vacuum chamber to de-gas the epoxy prior to casting to reduce bubbles, which can add to cost.
My guess is it would add up to the same as commissioning a blown borosilicate globe in the end.