I think Demon's Souls got a boost in popularity after Dark Souls came out... they extended the server life a million times, and as far as I know, it is still up!
The most finicky gamers I know say that Dark Souls is their favorite game, and that is why I am still their friend. Their tastes are otherwise a mile away, but we can talk about DS for hours. These powergamers fucking destroy everything they play, but Dark Souls still had a high enough ceiling for them. They immediately played Demon's Souls afterward, and said it was even harder...
Dark Souls 2 could be directed by Michael Bay and I'd still buy it. I will give money to the brand name even if the final product sucks, just this once.
Friend co-op sounds fun, despite how it would ruin the emotional desperation theme. I think the 3rd game in the series is the perfect time to implement such "what if" features. The gameplay mechanics are solid, but I don't think I'd appreciate any more invisible floors or 3 foot visibility dungeons, no matter how well designed. No need to beat a dead horse.
I would happily play capture the flag with my Dark Soul's character, to put it bluntly.