Yeah, not gonna say that US training arc can't happen, Deku will definitely go there one day, but that doesn't mean all hero students will.
What im hoping for the future:
Shigaraki take over Japan and the heroes must leave Japan because right now Shiggy has the control, it would explain the state of Deku "That day Heroes vanished from the city" in chapter 257.
Then I can see a Us training arc, also I hope that Endevour was just the number one of Japan and not from the world.
This could lead far more stronger heroes who could help the heroes from Japan, imagine Endevour was just one of the weakest Heroes(if we have 10Top Heroes overall the world).
It would probably even give Shiggy a reason to make more plans, to take over the world, not just japan.
As we see all the top heroes are in Japan but it was said that 80 of the Humans having power which means 6Billionen People should have power. But the most heroes(the top 10) which we see are just in japan even though overall the world we should have many heroes and villians. It make sense if just Endevour beeing the number one in Japan but not the strongest overall. Just look how easily Shiggy trash him away, let say Hori planning overall the world the top 10heroes, I can see the current number one hero for the whole world is still to much for Shiggy so he stay in Japan and building up his troup.
While all the heroes of Japan escape to Usa, Deku and the other training very hard under the number one of US who could probably the strongest Hero so far. And then in the final arc we see Shiggy/AllforOne trying to take the lead over the world and fighting off all heroes of the world.