Fairness disclaimer I haven't gotten into these things in at least two years but, isn't gijinka basically moe cosplaying?
Hmmm... apparently not, at least not by definition. But at least that's the impression I got after I went to scan for examples for comparison. And, even after checking the definition like five times, nothing makes it functionally different than basically cute child characters wearing elaborate fandom costumes.
Which, for a PMD, is a if not the dealbreaker.
See, when I read a PMD, the P is a very important part of the story. It's got to be about Pokémon - creatures with wildly divergent morphologies and environmental constraints trying to fit together. How they manage to work together, how having four legs instead of two, or one (Lileep) or none (Voltorb) effects their lives and their cultures. How have tactics and jobs adapted to the fact that some people can naturally fly whereas others can not. How relevant smell is compared to how relevant sight is for our world.
Compared to that, Pokémon gijinkas are simply humans - pretty homogeneous creatures functionally speaking - only this time, they are in costume and likely have superpowers. OH WAIT!!! So if I wanted to read about that kind of concept I could just have turned to Justice League or The X-Men, because they are about humans, and hey at least they tend to have good plots. The only artistic difference, depending on the medium, would be the moe factor.
Pokémorphs might have a better chance, since, if going deep enough into the concept, they tend to keep more of the Pokémon morphology into them rather than basically making it a costume, but down the line it crashes hard into the same issue, only with a better safety net. The problem is, most Pokémorph stuff I've seen is basically "human has this one or two Pokémon appendages" and it's just left at that, with no consequences and no better integration, so I wouldn't really expect much if anything about this particular subgenre. No one ever really speaks of how having say a Charmeleon's leg affects some very important stuff such as one's stance and gait, nor the taxation it would have on musculature of the lower spine. it's just "cool! Fire!" and on to next chapter. Let alone talk of how an otherwise completely human body can maintain that fire.
Also, either for "humans in costumes" or for "humans with extra body parts", societal constructs would not really change much. The resulting setting in terms of eg.: architecture, would simply end up being "our world but with weirder chairs" rather than "a Pokémon world".
Bottom line: I don't know if it can work, maybe someone can make it work, somehow. But if I am looking for Pokémon stories about Poḱémon, being Pokémon, in a setting of Pokémon, which is basically PMD's selling factor, then "humans in costumes" or "humans with animal parts" is gonna be an instant red flag.
