I’m more proposing the general idea to be adopted by other apps; just using my implementation as an example.

would it be possible to let the user add/remove options?

Add? Definitely (and fairly easily). Remove? Not so much (at least in my implementation). Those are the only 3 I know of right now that work reliably. If there are ever more than 3, I would probably move to a dynamic method where you’d just enable certain ones from a list (kind of like Searx-NG if you’re familiar with that). A user adding a custom one would work like adding a search provider to a browser (e.g. https://archiver.example.com/?url=%s)

In practice, I tend to need all 3 depending on the source URL in the post. Some don’t have a copy of the target or don’t render certain sources as well as others, so having a few to choose from is often needed. Allowing user-custom ones is a great idea though.

If you add a link in the menu to some fediverse post, people can suggest changes to the defaults, or exchange their personalizations

I sort-of do that already with suggestions for the built-in Invidious/Piped instances list, but ask that they be submitted via Github or the Tesseract Lemmy community (users can define their own Inv/Piped instances as of a few versions ago). Dunno if I’d want the link to that in the selector menu, but could easily link it from the settings panel where you’d hypothetically edit the archive sources.

Thanks for the feedback; I’ll probably work on adding support to at least add custom archive services in one of the next releases (and probably eventually work toward a fully customizable version).