Demon's Souls may very well get a sequel, and no it's not Project Dark per say.
SCE Japan Studio's Takeshi Kajii confirmed in an interview with the guardian that there are no plans for a sequel.
"At the moment, my answer is 'no sequel!'," he said.
"However, we have been encouraged by all the players, and this title is so well supported, and besides we like this title so much"¦ Well, this is my own feeling, but I think one day we could bring you another Demon's Souls..."
Demon's Souls is notorious for it's difficulty curve, but it has still garnered quite a following. Developer From Software is currently working on a little something called Project Dark, which honestly looks a lot like a Demon's Souls sequel.
Source: The Guardian