This would be huge for realtime gaming across continents.
You say sans routing latencies, but these are very much significant for intercontinental communication:
I get 6ms ping to AWS eu-central, which is less than 100km by air from me. I get 114ms to AWS us-east-1, which is roughly 6500km. Now 6500km / (2/3 * c) = ~32ms. So if there were a fibre running in a straight line, time in the fibre would be 32ms. Of course it isn't running in a straight line, so let's say 50ms are pure "light traveling through fibre". Switching all of that to hollow-core would cut that to 33ms, so that's a savings of 17ms or roughly 15% of my total latency.
This is still a very nice savings, but very far off from cutting latency in half.
(Also, it's a single hop from my company network to DE-CIX, one of the largest internet exchanges in the world, so I feel confident saying my results aren't skewed by a bad uplink.)