Add-in Developers - Automated Testing Platform
It is very difficult to test add-ins against multiple versions of Office and on different platforms.
For example, I ran into an issue where I had the latest macOS but a user had an older version. It was very difficult to debug and test code against that older version.
Therefore, it would be nice to have something like https://www.browserstack.com/ or Sauce Labs that was available to Add-in Developers so that we could run some automated testing in CI to make sure our changes will work on multiple platforms and environments. Maybe even at a minimum a set of VM's like what the Edge team provides to give users the ability to at least manually test against various platforms.