A crazy idea for a hack

[Velocd]

Now I don't think I would ever use something like this unless I beta tested it out many times, but it seems like a interesting idea. I'm more interested in general feedback about a strange idea like this.

Allow guests to post. But guests will be prompted before posting to enter a screen name/username, for their time on the boards. The forum will keep track of each individual guests post count, and say, at 20 posts (admin definable in the admin cp), the guest is automatically registered as a member under the screen name they first picked. As for a password, when they first hit 20 posts they could recieve a screen of some sort telling them they are now a member, and also a random password/ or maybe allow them to create a password right then and there. For those guests who maybe don't make it to 20 posts, say leave off at 12 and never post again, there could be some sort of guest cleaner that deletes all guests who have not posted within 3 (admin definable) days.

Just an interesting idea, I'm not sure how it would really work out, or the problems that might form, unless I try it myself.