I've created the extension in Bugzilla, but is there a codebase or at least repository somewhere, and a one-liner description of what this extension provides?
The extension homepage seems to be a redirect to an overview page...

I've created the extension in Bugzilla

Thank you.

but is there a codebase

• It is currently empty and will be filled during GSoC
• https://gerrit.wikimedia.org/r/mediawiki/extensions/MolHandler

one-liner description of what this extension provides

See above:

• MediaHandler for Chemical table files (preview rendering using the indigo toolkit)

Not sufficient? What else should I add?

The extension homepage seems to be a redirect to an overview page...

This will be changed now.

Thanks, that's all I needed.