I'm interested in doing the same thing on my site. I'd like to trigger different forms based on which product variant my custom selects.
So given 3 options for color patterns - Solid, Two Tone or 3 Tone - when they select "Solid" it will give them a list of the solid colors available. "Two Tone" would trigger a form for the two tone colors I have and "Three Tone" a third form that corresponds with the three tone colors available.
Much like DreamrW, I'm only doing this to get around the 250 Variant limit. Again, if there were a way around that I'd just run more variants.