I'm only picking on defender because it sends the most to me, but this would be great on all plugins.
A way to combine all of the emails for a single site in to one email, rather than 1000 a week I feel like I'm getting at the moment. All of defenders tweaks, checks and 'everything is ok' emails are an overload, especially as I want to be on top of these as much as possible.
A nice clean combined email on a set schedule would be amazing.
(I feel for this guy who seems to have the same problem and just wanted to know how to turn them off – https://premium.wpmudev.org/forums/topic/defender-sending-multiple-emails-)