I asked a similar question to many app devs maybe a year ago. The answer was mostly the same: it was considered as negative and breaking with the Nextcloud promises of a independent framework. In the end, I accepted that I will most probably have no statistics about the app usage, unfortunately.
I had although been given the hint that GitHub had some statistics on the number of downloads of the individual releases. This can be used at least to some extend.
Doing such surveys where you ask people to participate is nice to get a view on the community, especially when the survey is specific and the results are shared afterwards. Apps have also a section here on the forum, each developer can also ask for feedback.
For survey modules, some people will oppose to an automation to share more or less automatically data, you create such an infrastructure. If there is a bug they might share more than they want, … especially that might be one of the main reasons not to use big cloud providers.