There are a lot of web-based games, currently of course most of them from the fantasy genre. Nearly everything can be done, a lot has been done, but it is not that simple and easy to programm - if you want to make it good.
The main problem/difference between web-based and SEIV is the turn-based principle. Web-based games are pseudo-realtime, i.e. you have a certain number of minutes/hours and then the game advances to the next turn. There usually lies the weakness of these games: if you cannot attend them 24/7 you are just cannon fodder. You could do a game with long intervalls, like 24 hours, between turns, but what would the difference to PBW be then ?
