Not sure what you're getting at with the comment about PSL... PSL is a standardized central directory of domain suffixes that are known to have "end user specific subdomains or hosts", and my understanding is the lower domain limits do not apply to domains on the PSL. It has nothing to do with uncertified certs.
If you went that route you'd need to be sure to investigate the side effects though, as being on the PSL does have some behavioral effects on cookie access/etc. - generally to protect subdomains from each other.
Were you perhaps confusing this with the staging server?