Thanks. I didn't see that feature request (I searched for "nickname"). I don't think it is impossible with MSI, but you'll probably need customized actions. This post (https://developercommunity.visualstudio.com/solutions/21956/view.html) explains that any VS2017 gets a directory in
Code:C:\ProgramData\Microsoft\VisualStudio\Packages\_Instances\
Each directory has a unique hash value, but its subdir contains a state.json file, which includes the nickname of that installation, the base path, the extension path and everything else. Whether this is the easiest method to use, I don't know, but it at least appears to be conclusive, which is a good thing.
Meanwhile I'm totally fine with using the ZIP installer :).