From the perspective of a potential supporter (not me, generally), why would i go along with this? Dedicated patrons i guess. Who am i to judge? That's all.
Playing a bit of devil's advocate here, it is also rather risky for the creator to adopt this kind of model. While it's true that you technically doesn't need to waste time to mod something that nobody wants, as they crowdfunded it in advance, it would also mean that you're attracting much more one time patrons, those that either only crowdfund the headmod they wants, or those who only became patrons once said mod is on voting for release/released for lower tier patrons, rather than attracting much more monthly patrons who subbed because it's cheap enough that they can forget about the monthly bill.
But yeah, AAA games prices for a mod of unknown quality, yet Xyth is still doing it means it worked for them.