Feature summary

It would be less redundant and (to me) more intuitive if Module: didn't have to be repeated in the names of modules that are being tested using Special:TemplateSandbox.

Reasoning

Initially when I tried to test a custom version of Module:grc-conj with dependencies, I edited Module:User:Erutuon/grc-conj and I didn't understand why it didn't work. I gave up for a while, and then sometime later figured out that I had to move it to Module:User:Erutuon/Module:grc-conj. Now that I've done it once, I know what to do, but I still don't like the redundancy.

I am not sure why Module: has to be repeated in the title. Repetition is helpful for disambiguating wikitext templates (User:whatever/Template:template name) because there are usually other things at the top level of a person's User namespace besides modules. The repetition might not be necessary for Scribunto modules because they can only exist in the Module: namespace, and almost everything in the Module: namespace is a module except documentation pages, sanitized CSS, and JSON, and those are distinguishable by content model. (I tried creating User:Erutuon/module test and changing it to the Scribunto content model, but Scribunto wasn't on the list.)

Removing repetition would permit shorter titles for a set of modules that you want to test using Special:TemplateSandbox, and it's possible that other newbies to the template sandbox would not realize they need repeat the Module: and give up on using the feature, like me when I was first trying to use it.

Possible breakage

A problem is when there is a module that has the name of a documentation subpage. Documentation pages are wikitext and can't be used by Scribunto. On Wiktionary, documentation subpages are at /documentation and we have https://en.wiktionary.org/wiki/Module:documentation. Under this proposal the sandbox version would be situated at Module:User:Erutuon/documentation under this proposal, but that is actually a wikitext documentation page which can't be used by the template sandbox. I would propose the solution that the sandbox, when retrieving require("Module:documentation"), check for Module:sandbox_prefix/documentation and then Module:sandbox_prefix/Module:documentation and use the first one (if any) that is a Scribunto page.

Possibly not requiring the Module: duplication would change which sandbox modules are retrieved in real uses of the template sandbox. Perhaps there is a way to test this, even if there isn't a record of TemplateSandbox inputs, by finding prefixes before a Module: inside module titles and finding cases where a base-level module could be retrieved two different ways using that prefix.