I too really miss this as it was really handy that it stopped the iPad going to sleep so was more like the C4 touchscreen. I have an iPad in every room as a remote and to keep turning it back on is a nuisance. Also, you could leave it on the cameras and see if someone was coming up the drive.
The guided access is more to keep the iPad in one app but does not keep the screen turned on.
Anyone know if the dedicated mode is hidden somewhere?
Roo