Tho, to get to my point a simple co-op mode would be great, accompagnied with a little friends client-server system. A la Diablo II. A more worked out meeting place "say, all inn's act as some cross-client meeting place" would be nice, to have some roleplaying interaction with strangers. But this might not be feaseble in a simple manner.

and ofcourse modability.

you mean like guildwars ? well the citys are the meeting places, not really inn's or something similar.
that was a nice idea i thought at first, but i proved to be quite frustrating finding a good team. but like this it would become more a mmorpg offcourse.
yet it would be very nice to still be able to play single player RPG and at the same time have the possibility to meet your friends or complete strangers in inns or citys or special meeting places.
and make it possible to play together (either in a duel or arena competition or play quests together. but the quests should be made harder the bigger the team gets so it is challenging (not impossible) if you play alone
and also still challenging for a team.
but as i already said, it would become more of an MMORPG...

There is no spoon !