If the player is new or not paying attention, it will surprise them, maybe catastrophically. If the player knows what’s coming, they will want to spread their assets out but keep reserve troops and air in range so that when the Chinese storm down from the heavens they can be stopped. This will hamper their mobility and keep them worried and in a more defensive state.
With this plan you are giving up income from Chinese territories to the Japanese earlier, so you have to justify it by coordinating it so that when the Chinese descend there are other stacks around the map stepping it up at the same time and Japan can’t deal with everything at once.
As to why this play isn’t standard, I have found that the Chinese can actually do some good in the early stages of the game, especially against a J1. You just throw everything at Yunnan, move the Brits in there too. Sure the Japanese can smash you but they lose all their ground and a bunch of air. Mission accomplished. You can’t do anything else with the Chinese so you may as well use them as the breaker to the Japanese wave. You bring the Russians in too and if they decide to crush both stacks they’ve got nothing left for Calcutta.
My response as Japan would probably be to let the Russians have northern China in this scenario, at least for a few turns, and this is likely a better result than just holding everything back until America shows up. Maybe China can start saving up 3-8 IPC’s per turn once this has occurred instead of replacing their Yunnan stack and then come back with a vengeance mid-game.