I've been away and not had access to a posting-friendly computer for a few days, but something came to mind on my train ride home today.
First off - I've done that particular kind of forum RP before. I participated in an EV:Nova-themed one called "670 NC". (Assuming I remember the name right, anyway.) It was fun, but even though I knew two of the other participants personally from school and was often able to work with them directly on posts, and I had plenty of other stuff to do, waiting for other people to respond really could be painful.
Anyway - that specific style of RP? It might not be happening on the official forums, but people are already doing it every single day. Regularly. Can you guess where?
In channels. In real-time.
Every interaction is important and can have an impact on every other interaction that follows it, especially in an environment like the one that EVE provides. Look at it this way.
Let's say two characters meet up somewhere and talk. For whatever reason, some sort of meaningful ~thing~ happens or is said during that interaction that would color and influence those characters' interactions with themselves and others.
If that interaction happens in a chat channel, then the two players are immediately able to act upon what happened and use it elsewhere in other interactions, in real-time, as part of the universe.
On the other hand, if it played out in an RP-by-snail-mail forum thread? It could be days, weeks or even months before that impactful thing actually was written out and would become usable elsewhere, even though it technically happened quite a while before that in-universe.
Reconciling the two completely different timescales is difficult and incredibly unpleasant, especially when you KNOW something important and meaningful would have occurred during that scene, but don't know what it is yet because you haven't gotten there yet due to the nature of that RP style.
I'm not saying that the two methods are 100% incompatible, but when it comes down to it, one is a lot more compatible with EVE than the other: when there is an actual, living world that changes from day to day due to the interactions of the players, RP-by-snail-mail is approaching equivalency with shooting yourself in the foot RPwise. Perhaps in another game where the universe is largely stagnant and the players' actions have no effect on the world around them, it works better. But in EVE, you are generally going to be better off with the more real-time interaction you can get through channels and treating the IGS as an in-universe forum, than trying to old-skool it.