No, there is currently not a way to simply do this, so you have posted in the correct spot as this would count as a feature request.
“Simple Enough” compared to what? If you’re a programmer, feel free to code this and send it to me, and I’ll add it, otherwise it goes in here with all the other feature requests.
If you’re a non-programmer, then you simply don’t understand that what seems “simple enough” is anything but simple. Difficult? No, but not simple, as it requires quite a bit of code to go through every task in the task table, and compare against every signup in the signup table, and then figure out which tasks haven’t been completely filled yet, and then find the corresponding sheet from the sheet table in order to get the contacts for that sheet, and then have some kind of email template (which, of course, people will want to edit, so you have to add all those admin settings functions as well), and then put together each email one at a time and send them.
You can also read the following to see why I’m reluctant to continue to add new features (or just simply browse through the many many feature requests to see that there is simply no way to make everyone happy, as many people have their own ideas of what they think should be a feature):
https://stephensherrardplugins.com/support/topic/more-features-or-reworked-pro-version/