While developing them and getting them to the point you might be willing to send a pull request it makes sense to have a public space to put them . . . I’m in the same position trying to write a puppet plugin.
Also, small and simple is very relative to your skill levels!
I’m not sure about this part when it comes to Kakoune:
Vim-polyglot is generally more up to date / correct compared to the baked in scripts.
The problem I see here is overriding highlighters that is unfortunately not really as easy to do. Well, perhaps if such repo provides, say, C++ language highlighting, it could possibly drop highlighters that Kakoune declares and then provide it’s own, but it’s kinda ineffective way to do this. Vim has some ways to decide if syntax should be applied which isn’t as easy to do in Kakoune.