Sorry, but I'm gonna be a bit of a wet blanket. And is just my view...

Can't recall 100%, but I thought that the whole deal with the Nocturnes was that they didn't physically age beyond a certain point, that Kise was only an exception because she left the Nocturne home to help Ras fight the Archdemon? In which case, Ludwig can't age unless doing the same, which, being the last Nocturne, feels like a choice he wouldn't make in any short order. Given the full shift towards narrative cohesion of the MLs they've taken, we don't have any other MLs currently possible that would link to another world for an ML Ludwig and an associated full story. in other words, of the  heroes associated with Ludwig, do any have an alt world ML? ML Ludwig is likely to be only be a variant of the current Ludwig - the same way JKise is just Kise from the previous war. It's not impossible for an adult Ludwig ML to be created, just narratively not particularly likely given what we know.

Def scaling is actually a pretty good reference to his nickname and story. He's a pacifist who wants to solve problems through diplomacy and not war. So not scaling with attack is pretty dope.

ML Ray buff is fine. Yes, it isn't change much except "additional attack" add in but it mean he still can get another buff like other ML 5*. Also they can add new heroes to support venom similar to early Seaseria that weak and become meta after Ran and Peira released. I don't think venom can become meta but surely easier to use in the future.