Another admin based request for this plugin is network directed settings for sending email.
The concept is to provide the same sending methodology to all sites in the network, but that can still be (slightly) personalized on a site-by-site basis.
It's beneficial for a network to provide a sending service bundled with the mail plugin, making it easy to set up and reliable -- not to mention making it more secure. The scenario is the network provides an email sending service -- SendGrid or Mandrill/MailChimp -- and a stable sending address that's branded to the service, requiring a single SPF/DKIM cert at the network level. This means every site would have to have a sending address of firstname.lastname@example.org. BUT, each site should still maintain it's individuality by having a unique Sender Name ("Site Owner") and a unique reply to address ("email@example.com"). This way the email security mechanics are maintained, but the public face remains with the site owner.
MailPoet does it this way and it's very effective.
Currently, enewsletter requires the individual site, even in multisite, have a unique setup and sending methodology that has to be arranged by the user. There is no network umbrella. This makes network use much harder to adopt, as the majority of work is on the user's end. And, subsequently, a lot of work from the network support staff to help them get set up. In two years of use, this plugin was never adopted by users specifically because set up and sending methodology was on them. It's one reason why I had to drop the plugin.
By having the option to specify network level umbrella sending -- even on a site-by-site activation -- this plugin is elevated to a very effective tool for everyone.
P.S. I really hope you're planning to update this plugin soon. An effective network newsletter solution tied to Pro-Sites levels would be really awesome.