Thanks for your questions!
So, the desync issues which affected Path of Exile years ago were related to the net code - or how the game client communicated with the servers - not the physical hardware of the servers. With Predictive the client operates on the assumption that there’ll be 0% packet loss, no latency spikes, and the server will authorize every action. If you tell the client you’re moving to the left, it’ll show you your character moving at the same time that it sends the action to the server for approval. With Lockstep, the client sends the command to the server and waits for confirmation before the local simulation is updated to show your character taking that action. This rigidly keeps everything in sync, but has the trade-off that those with higher pings don’t have as good an experience - hence why GGG chose to keep Predictive mode available and gradually improve it rather than scrapping it and having everyone on Lockstep.
Please understand that the game’s net code is probably going to be something we iterate on over time, although this should mean the end result is better than if we created it once and then refused to touch it again. Avoiding desync problems will definitely be a priority.
Eleventh Hour Games are an international team - we’ll absolutely have servers outside the US! I can’t yet make any commitments for specific locations, however. If you asked me whether we’ll have servers in Europe, the answer would be yes. But if you asked whether we’ll use a data center in Paris or in Frankfurt, I honestly don’t know.