Ability to archive (rather than delete) channels
Teams is great, but there is a definite issue of number of channels ballooning to unsustainable levels. Therefore, we often go clean up and remove old channels, which require them to be deleted. However, then all the data is lost from those channels, so it's no longer possible to search for that data. If there was the option to archive rather than delete old channels, that data would remain available (and searchable).