The general plan is to keep traffic here, not send it elsewhere.
Then you should probably look into some way of keeping a character sheet that isn't just a plain text box. You might want to surf around and see what options other sites use for some of the more popular games.
For example, iPlay4e imports .dnd4e character sheets from the Character Builder, which is a big bonus for 4e players because you don't have to completely re-type your character.
I don't know if it's still alive, but there was a service called 3eProfiler that I used a few years ago to store 3.0 and 3.5 D&D sheets. I think they offered a download that webmasters could use to put a 3eProfiler on their own sites.
This is getting into the area of "may be too much trouble to be worth it" but you might want to consider finding some way of letting users build their own character sheet "templates". A template would basically be a bunch of text boxes, dropdowns, etc that users could lay out on their own and share with other users. So one player in a PbP game could put together a CS template for their chosen game system and share that template with the other players in the game.
If you want to get really advanced you could let template creators specify certain "actions" (or dice rolls) that can be automatically made using values from the template. For example, when playing a D&D 4e game you could create a template that stored the character's level, the 6 ability scores, and the ability score modifiers, then you could create an "action" called "Str attack" that would roll 1d20 and add whatever is in the Str Modifier field plus whatever is in the level field divided by 2. An alias using that character sheet could then fill out those values and then after they've made a post they could choose to add a roll and instead of rolling normally they could pick the "Str attack" action and it would automatically do the roll using the information taken from that alias's sheet.
I would be ecstatic if you implemented this sort of thing, but it would probably take a lot of code and might be comparable to the effort put into the Gamers Seeking Gamers system (if not more so).
I don't play PbPs often anymore, but honestly there are only two things that would make me want to store my character sheet on this site as opposed to elsewhere. One would be the ability to quickly import a sheet from elsewhere (like iPlay4e). The other would be the ability to use the information I typed in to automatically do dice rolls. If you don't provide either one of those things then I'm likely to just use the character sheet text box to paste in a link to some other site.
Not trying to be negative, just trying to point out that there are plenty of other sites out there that do a very good job of storing character sheets, and if you want people to use EN World for that then you'll need to either provide the same quality of sheet-storing or give us some feature the other sites don't have (like the ability to use numbers from the sheet in dice rolls).
