The delay is down to it being one of the "difficult" stories from the period. Many of the Pertwee episodes require extensive restoration and new technologies have been created from scratch to address the various issues (for example Reverse Standards Conversion and an entirely new way to identify and restore original color signals to monochrome recordings). There have been a few of these trouble spots already to hit DVD (the big ones are The Silurians and Inferno which, as you may have noticed just from watching the DVDs, are still somewhat ropey despite massive restoration work). I'm sure The Daemons is being held until they have the best possible restoration techniques since it is considered a crown jewel.
Return to Devil's End is almost certainly not going to be on the DVD as 2E (which makes them) has shown little interest in pursuing the licenses for this sort of material in the past. Unfortunately.