Alfa1, I find your idea very interesting. Do you actually apply it in your forum? or is it just a suggestion that still needs a modification?
The trick would be to guide them through registration, after they submit their post. If they do not complete registration, then their posts are removed from the database. But as they have already posted, they are very likely to complete registration. IPB has an instant username check function, so there would not be any duplicate user names.
Anyway, I probably should not have mentioned the idea, as its getting too far off topic. Once I have access to the suggestion forums, I can post a write up there and see what people think of it. Or just have the functionality coded for me.
If you do use it, please let us know how to apply it. For example, how do you direct the guest, after posting, to the page telling them to reigister for their post to show up? and how do you make their post deleted if they didn't register? and how do you make the post visible once they register?