Isn't that going to kill performance (and possibly even kill the system, in the event of partial netsplits or similar)?

That sounds... interesting. So if A1 is on a different segment, but has a faster link (less congestion?) to A3, than A2, even if it takes 1000t time to send the first message from A1 to A2, and only 10t+t time = 11t time to send a message, from A1 to A3, and from A3 to A2 -- the plan is to guarantee ordering of messages m1, m3 at A2 (delaying m1 at least 989t)?

How will Pony achieve this in a distributed context? Isn't this essentially asking for exactly-once delivery?

How do you intend to achieve this?