Hi Sven Jost big apologies for the delay in replying and thank you for contributing.
I'm not familiar with the Windows upload requirements in AppCenter but from a quick look at https://docs.microsoft.com/en-us/appcenter/distribution/uploading#windows it appears that there are multiple file formats of which zip is just one - appx, .appxbundle, .appxupload, .msi, .msix, .msixbundle, .msixupload, or .zip.
That's quite a few formats that I don't understand the implications of as I don't develop for Windows. I think the best thing to do is to limit the scope of this to only support zips for now and gradually add extra support in the future.
Having said that I'll make some minor changes to your branch and push them but am still in the processes of evaluating the changes so I don't know exactly when these can be released.