Gonna be honest here.
This is going to be quite a tricky job for Vieira, I doubt he can match up to what Hodgson did turning them from a side fighting relegation to a solid mid-table outfit. Because due to their ceiling you'd imagine their limit is about 10th at best and even then there's a lot of competition these days to finish top half. So if he's hovering around 15th or so Palace fans might start getting unhappy especially if the football isn't the best. I can't see Vieira really doing much to enhance his reputation tbh.
That said knowing how we work even doing a remotely competent job might be enough for him to get the Arsenal gig.
Avoiding relegation would be a success. Suicide mission. All the best, though.