Can I use the first value of a multivalue field as another field? ("Cover" use case)
I'm not aware of a "wrapper" field type, but you have a few options.

I've done the same myself in Views by filtering by the "delta" value, which is the individual values in a multivalue field. That way it's easy to require "delta = 0" and get the first value. This has a limitation of currently not working with arguments/contextual filters though.

A second option is the to ctools recently added support for delta values. You can render a field and set both offset, range and reversal of deltas.

Final option I can think of is Computed Field, which could be programmatically coded to act as field wrapper.