HyperDex performs best in a single-datacenter environment. You are right that synchronous replication between datacenters can (and likely will) be slow.
There's much work on this (my favorites are Walter and COPS from SOSP 11) that is on-going. We'll likely be throwing our hat into the ring soon as well.
You are right that pushing some logic to the "thick client" is one of the viable solutions.
Feel free to contact us as you work on your PoC. We'd love to hear about positive results and help with any rough patches you encounter.
There's much work on this (my favorites are Walter and COPS from SOSP 11) that is on-going. We'll likely be throwing our hat into the ring soon as well.
You are right that pushing some logic to the "thick client" is one of the viable solutions.
Feel free to contact us as you work on your PoC. We'd love to hear about positive results and help with any rough patches you encounter.