Adressing multiple list

One of my preconditions to use Newsletter module is the possibility for one newsletter to be send to multiple newsletters.
It seems it is not possible to choose multiple 'Subscriber List' when a fresh newsletter is created.
I wonder if it is possible that 'Subscriber List' field become a multi-select control to choose more than one list per newsletter.
Please let me know if this feature could be implemented in Newsletter module.

Thanks, Bertrand

N.B: The other precondition is to be able to have a File attachment. This point is already posted as a feature request.