Allow installing older versions of Xamarin in Visual Studio 2017
This is needed in case of buggy Xamarin releases that happen quite often, sadly. There's no way to go back and install the previous version without downgrading entire VS2017. The way it was in VS2015 was really convenient.
Michael Rumpler commented
Additional to the channel selection I'd propose that the channel only preselects a specific version for each product, but that the user can still overrule the version which will be installed. This would allow to easily install any previous/alpha/beta version of any product. Of course such manually selected combinations cannot be supported, but this would lie in the responsibility of the user.