Hi there,
Our view on this when it has come up in the past is that it is not supported due to risks of cluster partition. The diversity of failure modes makes it an option we would not encourage - as @SpindleNinja points out, the cluster quorum marker may end up in a different room to the surviving nodes, which would cause them to also shut down. So instead of reducing risk, you're actually increasing it.
If you are interested in geographic diversity, even within the same building, we have an option called Metrocluster, which deploys identically configured systems in two locations (with options of a tiebreaker in a third), using IP connectivity, and as of 9.6 it can run on our most cost effective systems, the FAS2750/AFFA220 nodes.
It doesn't work with 6 node environments, and in almost all cases should be set up at install time, so the best deployment options for it would be a new environment to install and migrate highly critical workloads to. We have some more information at (business) https://www.netapp.com/us/products/backup-recovery/metrocluster-bcdr.aspx and (technical) https://www.netapp.com/us/media/tr-4705.pdf Please send me a message either here or via my first.last @ netapp. com email with your corporate contact details if you'd like your NetApp account manager to reach out with more details.
Hope this helps!