It would hurt founders' perceptions but wouldn't actually decrease any individual founder's chances of success. YC would just accept a bunch of people who aren't likely to get funded.
What would happen if you split up the batches into two groups, YC Classic and YC Black Swan, and placed founders into the groups post-interview? People who were placed in YC Classic could continue to have the expectation of ~100% demo day success they do now, while the people placed in YC Black Swan would be told "I find your idea interesting and we'll let you in but don't expect funding after demo day." People could take the Black Swan offers as rejections if they wanted.
There are a bunch of problems with this approach, but I wouldn't be totally surprised if way more than 30% of YC Black Swan was funded.
What would happen if you split up the batches into two groups, YC Classic and YC Black Swan, and placed founders into the groups post-interview? People who were placed in YC Classic could continue to have the expectation of ~100% demo day success they do now, while the people placed in YC Black Swan would be told "I find your idea interesting and we'll let you in but don't expect funding after demo day." People could take the Black Swan offers as rejections if they wanted.
There are a bunch of problems with this approach, but I wouldn't be totally surprised if way more than 30% of YC Black Swan was funded.