Wonder about this myself, have noticed with folks like Rob Walling and presumably others. They all seem to suggest testing market fit by essentially doing this for features, and in some cases soft launching websites prior to having anything ready at all!
Seems risky if you are dipping your toes into something you do not have a deep understanding of the product market for.
Anecdotally I've seen with video games (the communities tends to be very vocal and somewhat centralized?), where inexperienced developers promise things that are realistically way beyond the capabilities, or promise things too early based on their honeymoon period for rough implementations. Then suffer on the other end when they fail to meet roadmaps or delivery of features at all.
It seems like an even worse situation with serious software with asks for larger amounts of money? Then again maybe this strategy can get away with it, because there is that lack of cohesive communities with some degree of group think who would get up in arms over bad promises?
The reason it won't really work for gamedev or complex software is that the risk of the business isn't really in the product-market fit, but rather in stellar execution.
If your business idea is dependent on being able to do a complicated thing, then a POC or a demo might make more sense for testing the waters and seeing if there's any technical impediment to the idea