I would like to use the same SRs on XenServer hosts that are not able to be part of the same pool (because of not having the exact same cpu feature set, if I understand it correctly) in order to share templates, being able to (manually) start a host on another node, backing up running hosts on other hardware etc etc. The technology for SR can be any of iSCSI, NFS or CIFS, iSCSI would obviously be preferred.
Trying to add an iSCSI volume renders a "This LUN is already in use as SR iSCSI - Shared Storage on pool xxxxxx.". Adding a NFS share on one XS host, creating a template there and then checking another XS host reveals they don't agree on used space etc.
Coming from a vSphere world this is quite baffling, but if these are limitations then I will have to rethink some of the concepts for this low budget project.