Offer clear error messages for archive types not supported
Say you open a .ZIP file that is password protected, and you don't know it is password protected. Say you never had to use file-roller. You may wonder, why are ZIP files suddenly not supported? I think the text needs to be a lot more explicit about what is going on.
The other problem with this is that when you try to open any other file Nautilus opens the assigned app, I don't think most users are going to understand why this dialog is going to be thrown at their face, so saying "unsupported file type" is going to be a bit scary and prone to cause uncertainty to the user.
If this is always going to be a case of archives that we only support partially, I would be very explicit as to which feature we don't support in the message, something along the lines of "Files does not support password protected ZIP archives, please select an application that does"
Do we know all the possible reasons why autoar might not support a file type that it claims to support? If it is just about password protected ZIP and 7zip archives, we might be able to create different MIME types for those by trying to find a better magic match and just not let Nautilus claim MIME support for files it doesn't support.
Even then it is kind of a shitty experience, since most users might not know which apps would allow them to open the file, plus, they might not have any of the apps installed. How far is autoar from fully supporting these formats?