I'll be honest, we have seen many elemental variations of enemies in the game, and so far, we've not seen a hydro hilichurl. Maybe down the line, we may see a hilichurl that specializes in dealing with dendro damage. But it's all speculation from my end because ultimately, it depends on how Hoyoverse, creator of Genshin impact, plans to approach the game in the future and create new enemies. It all comes down to a better gameplay experience and the thrill of combat with enemies. And I'm pretty sure Hoyoverse has some good plans for this game in the future and won't disappoint players in the longer run. Being a day one player has gone through some ups and downs in terms of the content game has to offer, but so far, I'm pretty satisfied with it because I prefer to have more casual gameplay. However, I spend most of the time doing spiral abyss on my friend's accounts.