One minor problem I can foresee. Say I have $800 to burn, and want to put it toward sculpting the PME-D-TR3 PotatoMech from XTRO: REALLY Deep Periphery. It gets on the poll but gets zero votes, because even I might not vote for that. Problem is, of the six designs that do pass, I don't care about them and don't wish to donate my money. So I drop my $800 on online sellers who deeply discount their minis, and I get a better deal. So there's $800 that is not going into the project, and one more mini not being made for the three fans who want it.
I understand limiting the flow of incoming stuff to a manageable level, but at some point this scenario will occur. I don't have a realistic suggestion other than to maybe keep a slot open for people who want to wholly fund a specific mini themselves. I'd just rather see the money go directly to IWM.