i use ps on a daily professional bases mainly for post image editing. so ps on a mobile device is something i personally wont be interested in when i can do so much more in ps on my desktop.
as for drawing and painting, as mentioned, apps like procreate, sketchbook pro, artrage, Auryn Ink etc etc are more suited for mobile art me thinks.
i dont think we're too far behind the day when the ipad can be used like a wacom. not yet tho.