Hope you all don't mind a separate post for this but I felt it would get lost and be out of sight in my Retropie / KODI post.
So here is a link to my Rasplex / RetroPie dual-boot installer:
https://drive.google.com/file/d/0B1ZwtI ... sp=sharing
And a video of it in action:
https://www.youtube.com/watch?v=jFP6THVNLWY
It uses NOOBS to install both partitions and provides seamless switching between both operating systems. I created a Plex theme and designed a Rasplex logo myself, as the ones I found on the net didn't quite fit right in Emulation Station.
Its worth noting that Rasplex, whilst fundamentally based on OpenELEC, does not contain all the same functionality as OpenELEC does, in fact OpenELEC can directly use 'Bash' scripts where Rasplex uses 'Python'. This means that the script I created to switch over to RetroPie from within Rasplex is not as 'fancy' as the script I made for use in KODI (OpenELEC). It still does its job, and does it fine, but there is no message displayed or anything like that, its just a case of clicking on 'Games' and you boot straight into RetroPie, as shown in the video. Nothing wrong with that, just not as snazzy as I would have liked.

Please read the readme file for full instructions on how to install etc. but in case you are the type who doesn't read readme files then please do not change the skin in Rasplex!! If you change the skin from 'Aeon' which I have purposely set then you will lose the script to boot into RetroPie and be stuck in Rasplex for everrrrrrrr....
Anyway - I hope you find this useful. There are no other alternatives to Rasplex dual-booting as far as I can see, so this is probably your only option!


All the best.
Steve