Hi Sean,
First up, I do not know the characteristics of the environment you are dealing with nor do I know all the requirements but, this looks like a pretty decent solution.
I don't think you should over-engineer this when it comes to the PSC's. I mean, how likely is it that both PSC's are going to be down in one site? If this happens you probably have a larger outage where the vCenter or even the site is down anyway. If you just make sure you have HA enabled and the anty-affinity rules set for the PSC's you should be fine.
I do want to recommend the use of a ring topology for the PSC's, that way you don't have a single point of failure when it comes to PSC replication. Normally a PSC only replicates with one parter with a ring topology this becomes two parters. Basically you install the PSC's in a specific order and on the last one you change the replication parter to point back at the first one. See this KB on how to do this: https://kb.vmware.com/kb/2127057.
Hope this helps.
Regards,
Wesley