However, I feel that you might be jumping in too soon without all the details.
I feel that you should provide a suggested process and let the developers help with some of the decisions.
You don't want to end up with something that is not useful to most of the developers because you didn't understand all the ways that they need it.
I would suggest a page somewhere that outlines how you plan on building it and how it will work. Then list somewhere where developers can post suggestions or concerns.
Some example questions to be considering:
1. How will I be switching between the two? Different ports can be useful to most, but I don't like using other ports besides 80 so can I switch Apache and Nginx on port 80.
2. Will there be templates for nginx site configuration files. I really need the ability to alter the site configuration. I would prefer a Template file that I can modify that has variables in it that I can use like {{documentroot}} and {{domains}} etc.
3. Will PHP-FPM be part if this and will I be able to configure a template for the PHP-FPM files.