A setting like this could definitely be useful for both new and power users. I can’t think of many times I would personally want to tag over 100 files at once and, if I am, it is more likely a mistake. If you can choose to ignore it forever after the first warning, I think that would probably be a good compromise for power users.
For the larger picture, I agree that it’s very difficult to create simple, yet comprehensive, UI/UX for an application that, by its nature, is very complex. A good portion of the work I do centers around designing, developing and teaching libraries and museums how to use open-source technologies. The people I work with range from complete computer beginners to people who are pretty comfortable in a convoluted UI because they manage digital collections and it’s what they’re used to. 3D printing is a pretty good example of needing to have a thousand features for power users, while maintaining a simple, streamlined interface for new users.
Cura, I think, is a good example of trying to toe the line between new and experienced users. The print settings menu defaults to a very simplified interface and uses default settings. You can also tweak specific settings, if you are more comfortable with 3D printing. Even further, you can tweak how ‘advanced’ you want your custom settings window. Each setting comes with a tooltip to slowly introduce you to the new concepts. A lot of the people I have worked with respond well to this kind of interface, where you can pick your level of comfort, but it doesn’t leave you completely in the dark if you need to make custom ‘advanced’ tweaks.
Picard is obviously not a 3D printer slicer and a very different beast than Cura. Having a way to simplify the interface could help bridge the gap and provide some guard rails for new users. With or without a wizard-type interface, I think less buttons overall at one time might be a little less intimidating.
Another open-source app I use sometimes is OpenShot video editor. It has a menu bar open that switches between a ‘simple’ and ‘advanced’ window view. This approach usually amounts to some panes being open while others aren’t. An extension of this could be the ability to choose between ‘workflows’, such as adding/matching, tagging/renaming, submitting AcoustIDs, etc. Cura does similar by having workflow tabs for setting up a print, previewing it, then monitoring it through the print job.
It’s not open source, but Premiere Pro is pretty good at workflows.
Maybe I’m overthinking it! This would obviously be a huge change with a long design process, if there was even interest, but I thought I’d give my two-cents.