UploadWizard is extremely tuned for commons' use, and doesn't seem suitable for external use.

-1.

Can we get a more in-depth analysis and discussion on the rejection of UploadWizard?
UploadWizard has a configuration variable that disables the "Learn" section, which is the only part that's really obviously tied to commons. Without it, it looks just fine in any wiki:

There's other reasons UploadWizard is great for a wiki community:

• Broken into easy steps, the Wizard makes sure the user has proper permission to actually upload the image.
• the wizard helps identify the correct licensing information to attach to the image, something often omitted by casual contributors.
• In the case that the work is the uploader's own, the wizard explicitly has them release it under the wiki's license.
• In realtime, the wizard identifies unspecific or previously taken (conflicting) filenames.
• The wizard encourages informative descriptions to accompany each uploaded file. This is part of the standard file upload, but it is shown with the rest of the upload process all at once, making more users omit it. With this as an isolated step, it seems less daunting a task just to upload a single image, and indeed, contributors have responded to this.
• In the same place, encourages adding categories to the file, with an autocompleting box.
• files are uploaded right away, before asking for metadata. this way you can focus on the metadata, being sure your upload is going to be accepted in the first place.
• there is a link to use the old form, if users prefer for some reason.
• the admins can require file descriptions and other metadata, to prevent lots of low-quality uploads.
• the wizard of course concludes with a handy copy-paste box for using your images right away.

I can help you guys install UploadWizard if you want. It's easy.
I believe it will one day be the File Upload page, built into MediaWiki. It's already miles beyond the standard page. Until then, however, we have the extension.

Echoing @Truth from above, I would appreciate some insight into the reasons behind the decline here. I cannot find another extension that provides the functionality of UploadWizard, notably the ability to prompt the user for multiple fields to go in a description or attribution template at the same time as they are uploading the file.

@revi is there any part of UploadWizard other than the Learn section, which can be disabled, that inextricably ties it to Commons?

Just to note I have reversed the decision to decline this (after talking with other members of MWE), after taking another look at it, it didn't seem to Wikimedia specific, at least no more than a few of our other extensions. It has now been installed and is available from Special:ManageWiki/extensions. We may need to further adjust configuration later own to more Miraheze stuff but for now it is available with most default configuration.