Is it possible to see the @namespace header value of (other) installed userscripts?

Question

I know it is possible for a Greasemonkey/Tampermonkey userscript to access it's own header data from GM_info.

But is it possible for a userscript (or any other code) to get this information for another installed userscript?

Answer 1

No.
A userscript can only see its own information. And due to both security concerns and lack of perceived need, that is unlikely to change.

In theory, you could write a full browser extension/plugin that could read the Greasemonkey/Tampermonkey config files and extract that information, but that would be way more effort than it's worth.