From Kbps, to Mbps, to Gbps, we will, one day have Tbps. When do you think we will attain a speed that, it no longer makes sense to have anything faster?
Mbps/Gbps/Tbps is the bandwidth speed, instead of the physical speed of electromagnetic wave. You can always make more fibers and codecs and have them in parallel to get a greater bandwidth speed, which has no maximum limit. It all depends on how fast we need and how economically effective it is.
Never. As long as media increases in size (and it will - we will always want better quality) the broadband speeds will need to increase too.
I think you are mixing up throughput with latency. Can you confirm that you're not?
To further elaborate, there's always going to be flows that require large units. Like a link between EU and the US.