Why isn't an image field supported as a custom field?

I am wanting to create a custom field called "background image" to help users customize individual pages.

The best way to do this I would assume would be to use the CustomPress then create a custom field of an image type...the problem is that doesn't exist.

It appears that for years users have been requesting this feature...is there an eta?

The best way I can see to accomplish this is to use the plugin: http://www.advancedcustomfields.com/ , however the multi-user management features aren't a part of this plugin.

One could set up fields with this the "advanced custom field" plugin, then create a blog template with these new fields in place. However, if I wanted to introduce a new field image field to all my multi-site users, there is no way to update all the sites with a new field with the exception of doing it site by site.

Is there something I am missing with the CustomPress plugin, or is there another approach I should be taking with another plugin in the wpmudev eco system?

Thanks for the help.