Due to poor sales of DS3, 4 has been cancelled and the series put on hold.
http://www.oxm.co.uk/50813/ea-cancels-dead-space-4-following-dead-space-3-disappointment-rumour/
http://www.oxm.co.uk/50813/ea-cancels-dead-space-4-following-dead-space-3-disappointment-rumour/