Here's some rules a MMORPG should follow to maintain a PnP style.
1. Naming must have realistic names (from a list if really needed), and must be capable of having multiple same-name characters.
2. RP'ing is mandatory on specific RP servers/channels.
3. Questing with few uniques/procedural uniques. A-la Mythos?
4. The rules must be based on PnP, not more traditional CRPG (except if they are, of course, PnP inspired).
5. Procedural generation. Have each machine make a little bit of town.
Now, granted, I don't play any PnP RPG's (I would, but I don't have anyone to play with), my closest experience being Classic Battletech, but that's Wargaming.
I've read through the rules of most of the free systems, and played a lot of roguelikes, though. I'm working on a Parkour and Cyberpunk inspired PnP game. Hopefully it'll be simple enough to play blind.