I don't have a huge breadth of experience in the arena, but I play a decent amount of the Frozen match 3 (and it's predecessor). I think Russ's studio did those? Anyhow, I like the power ups they use and the methodology for earning them. As for collapsing... the lack of a firm grid certainly makes it a tough problem, though I don't understand the data structure issue. The distance based approach sounds novel, however... seems like any solution should leverage that rather than fight it. Could be a differentiating feature.
I'll give it some deeper thought and get back to ya!