When I read this posts, I think of theDash as a nice sleep hacking device. It is a wireless in-ear headphone with plenty of sensors (including HR, spo2 and movement). It is comfortable enough to sleep with it in the ears (I tried it, being developer backer). When they finally release the SDK and it would be really that easy that REM could be detected by an increase of HR plus little to no motion (due to SP) it can be modded to detect REM and and play sound during REM. You then can use any app-able vibration band (MiBand, iWatch, Android wear, ...) to deliver vibration cues.
(and thanks for the ecg paper!)