Generally speaking, the original usage of 'literacy' to describe posts/skill level meant more about a players ability to create quality than long posts (although long=good is a common misconception).
Literate/Illiterate, outside their original definitions (a person who is able/unable to read or write) are kind of dirty words here, since they can give the impression that a person who is 'illiterate' is not good enough for you, or that you can't really call what they do 'writing'. Similarly "Literate only" can come off as a sort of elitist flag; we prefer to be more specific about what we like in a post. For instance, instead of using the 'literate' catchall, you could say
"I like to write and read long posts that give me lots to respond to. Fluff is fine, and I love very detailed descriptions; lets give some depth to this story!"
or
"I like posts that give a lot to respond to. Please feel welcome to bring in NPCs or start events for our characters to react to, or even just be good with description about what your character is doing/what's going on around them"
One of these is more concerned with long, immersive posts, and the other just wants a good handle on what's happening so they know how to respond. Both could describe themselves as 'literate', but these give a better, less judgemental insight to other players about what they look for.
Similarly, instead of saying 'Illiterate players welcome" or "illiterate-semi-lit levels", you could say
"I don't really care about post length or what you include in your post, just participate in the story."
Again, more specific, better communication, nobody feels judged.
By valuing this kind of communication,we've created a more inclusive society
/thread lol