Is there anyone that has tried a full installation of the content delivery with XPM in Java 8? I know the prerequisites state that Java 7 is required, but I would like to know if anyone tried and manage to get it running under 8
Haven't tried to install using Java 8 and is possible that the installation still works, but regardless if works or not, if you face any issues there is a big chance that your implementation is not going to be supported as didn't follow the prerequisites.
If there is a valid reason for install in Java 8 because specific technical requirements of the customer, my recommendation is to ask the question formally throughout SDL Customer Support and see which options your implementation has of still being supported.
If there is no valid reason for install in Java 8, my recommendation is to use the documented and supported prerequisites.