give more details about, and word-processor functions to, moves/narrations
this includes, but is not limited to:
a running word counter at all times while you're typing a move, rather than the "x words left" that currently exists.
a note of how many words any individual move is, so people can get a better idea of what x words looks like before making a move.
buttons for italics, bold, etc, rather than memorization of formatting, even if said buttons just input the formatting necessary (i.e. asterisks, carrots, dashes, etc) for you.
Toby Currie commented
In general, I like that Storium is a bit bare bones at times. It makes the site easy to follow and learn. However, one of the biggest "but"s I have to that is the lack of information you have while making a move. I personally have to keep a tab of "Storium formatting" and a Word Counting website tab open whenever making a move, constantly switching between the three (including the move itself), which can disrupt the process.
It can also be difficult to plan a move out if you don't know how close you are to the word limit until you're TOO close. I've had moves where I'm not even halfway through what I was intending to write before the word limit jumps on me, and I have to rethink the whole move to account for that. Keeping track of word count as you write from the start will help to alleviate that from happening.