[mhurron]

It would instantly be forked and have the payment nag removed within 24 hours of it being open sourced by someone who is not willing to pay for it but still wants that nag removed. And they wouldn't be the only person to use that fork.

I doubt it would be a very good move for the author.

[gravypod]

Payment nagging isn't really acceptable for an application in general for free software. Just give the source distribution to anyone who pays for it and require copy-left changes.