Different content per user, not per user role

Hi,

First of all, thank you for this easy-to-use plugin! I am currently developing a website where I would need the content to be restricted to particular users, not to user groups. The perfect solution would be to have a meta box for each post with a list of subscriber-level users and checkboxes to select which user has access to this specific content and changing this setting would also trigger an e-mail to the user, that new content is available. Would that be possible using your plugin? Maybe with some premium add-ons or theme-level modifications?

Best regards,
Michal