Can vB4 be modified like this?
 

I understand that vBulletin is highly customizable. The software already has the built-in functionality to send an email to a user with new each post to a thread that they are subscribed to. The user can set their account to receive those emails per week, per day or per post.

Could a skilled PHP/SQL developer modify the vBulletin code to add an option where a user could choose to have all posts or new thread starts sent to that user (whether they are subscribed to that thread or not) in a daily email that also includes the contents of those postings. I would think that since the code is practically in place to do this so the modification would not be that difficult - assuming this kind of code modifications is possible.
and

Could this be done? (again, assuming a skilled PHP/SQL developer does the work?)

Anything is possible by a skilled coder.

You will want to think about what this would do to your server if you have a lot of users that are all getting emails about new threads and posts in several forums.

Thanks Lynne,

That's what I was hoping to hear.

It is only one forum and the group only makes between 1-15 posts per day (usually 7-8) and many (most?) of the members of the group will not want that "email me everything" feature enabled so I don't think that it will stress the server too severely.