The only problem with having it on the player's profile is, what if their status is different in different games?
Although I guess since there is a list of games you're playing on your profile, you could just have a colored dot next to each of them.

Still, I find that it would be super useful to know *who* someone is waiting for, which color coding does not provide; but maybe if there was a basic status that was easily changed, plus an optional way to add more detail?

This is a great idea and could really help narrators and players get a sense of why there might be a delay in someone's posts.

It might be nice if this could be implemented on a player’s profile. Even something as simple as a color indicator—green means active and frequently posting, yellow would be something like active, but busy, blue could be currently inactive at present (I’m not a fan of using red). That way every person could easily change their status and the change could be viewable by everyone.

Using the comments to let people know ahead of time if you're going to be going on vacation or busy studying for finals next week still seems like a good idea. However, a status indicator would be really helpful in that it lets the other players know what it is you're waiting for before making your next move. Or in fast-moving games, whether you're in the middle of typing something. It simply gives you a better idea of the other players' expectations and what you can expect from them.

Instead of having to wonder *why* someone's not responding when you expected them to, you could just mouse over their cast picture and read: "busy with work 'til tomorrow, I'll post as soon as I can" or "waiting for Player X to answer my question about dwarfs" or "still hanging from this cliff by my fingertips - someone toss me a rope already!".