I'm not exactly a crypto expert, just someone who pays attention to this kind of stuff, so I might be incorrect or have some misconceptions, but even that paper's justification agrees that there are possible outcomes where a stronger curve could prevail in the face of a weakness of Ed25519.

There are certainly scenarios where "all crypto becomes invalid" or "ECC becomes invalid" or "curves similar to Ed25519 become invalid", but with Defense In Depth... if all other things are equal, a stronger curve is better, and that is effectively the case here. The only downside of Ed448 that I'm aware of is a slight performance penalty, which is irrelevant in most applications, so there's no reason to actively choose a weaker curve. The "overkill" option is the sensible option in most cases.

AFAIK, no one is actually encrypting large sums of data using an asymmetric algorithm like we're discussing. It's typically just used to encrypt a symmetric key, which is then lightning fast to use on the bulk of the data. The performance of the asymmetric algorithm is only important in very specific scenarios.

I also believe that "no one" uses Ed448 in much the same way that "no one" uses JPEG XL; a lack of ecosystem support drastically hinders adoption, and it has nothing to do with people believing that Ed448 has no advantage over Ed25519. But, that's just like, my opinion. JPEG XL would be drastically better than the other image format options, but ecosystem support is a chicken and egg problem. Measuring the existing adoption of a poorly supported option doesn't give much insight. If people appreciate Ed25519 (and they really seem to), then offering the stronger version of Ed25519 seems like an obvious next step, even though it is a lot of work (which is why my original comment mentioned future proofing the API, but you seem to indicate that it is, so that's good). If the option existed and were exactly as easy to use, then why wouldn't people pick it for projects where the curve is open for selection?