If you could provide similar functionality / workloads as the old MS Small Business Server isn't there a MSP / reseller market opportunity? Self hosting for businesses that are < 25 users. They still tend to be serviced by small MSP. They've gone cloud because that's where their vendors went. Many hate it.

You'd need

* Directory/Authenticaion

* Email

* Shared Folders

* Wiki / Web something

If there were options for adding IM, PBX, CRM it could be a compelling offering for resellers.