@Jonah_Marsden It’s not exactly what you were requesting but this may be at least a little helpful until the MainWP Child Plugin evolves. There is also the Import Sites feature that you may edit with your Child Sites connection details and auto add them to the MainWP Dashboard - if you have not already considered this.
Considering that the MainWP White Label Extension already exists to take care of the MainWP Child Plugin Branding - In order to make this request a lot easier to pull off, I am making my personal MainWP Child Auto Downloader plugin repository PUBLIC. You may set this plugin up and offer it as a “Downloadable” for your services.
You may download and customize it as you would like here: