That’s actually a very good point. At ownCloud there is a proprietary self developed web app used by the employed QA team.
The platform basically allows you to select a branch / pull request and it starts a new docker container on the internet for you and within a few seconds you can access your test instance at {identifier}.foo.com.
I think it makes very much sense to build up something like that as well. But certainly as open-source, plus we need to make some more thoughts on who is hosting the platform… Whether everybody should have access, after all they can do all kind of mischief with the platform etc…
Probably some kind of GitHub login like we have in the forum and a check whether the user is a member of the Nextcloud community would solve such a problem.