Assuming these cables cost more, or require equipment that costs more, I wouldn't expect this on last mile connections. ISPs simply don't care that much. DSL providers typically run connections with settings that add 15+ms of round trip. My DSL provider runs PPPoE for fiber connections where fiber is available, etc. When I was on AT&T fiber, it was still about 3-5 ms round trip to the first hop. It's been a while since I've experienced cable to know how they mess it up.

If there's significant deployment of the cable in long distance networks, eventually that should trickle down to users. It would probably happen faster if there were competitive local networks, but regardless, a significant drop in latency across a country or ocean can be big enough to justify some expense.