Elrozin is toying with the idea of brevity. If it works for Earnest Hemingway (though I never understood why)...
Stagnating RP can be frustrating and potentially fatal for a character. However, creating a separate forum for offline RP would indirectly injure your own enjoyment.
If this were the case, people would log on for a while and, if their target doesn't show up, would lean on the forum. While this may potentially get things moving, it would remove from RP the 'living' world around you. It would impact the feeling of reality by diminishing things like emotes and the ever-present possibility of an immortal decided to pop in.
This may also negatively impact player numbers, which would make running around in game far less enjoyable for you since there'd be fewer people around.