Unfortunately vertical farming is mostly used for vegetables and fruits. Those command higher prices and need to be fresh. So placing the farm closer to the final customer in the city makes more sense. Right now vertical farms still have their expenses and even with LED lighting it isn't viable for some (cheaper) crops. I think for grains what's more likely to happen is denser cultivation and crops which can be harvested more often. Another possibility is crops which can grow on marginal land which previously wasn't possible to use for growing beforehand. China is already working on things like that.
Tbh... land or how close it is to the customer isn’t a big issue with potential new methods of grain farming using methods such as hydroponics... for example there are some efforts in Japan, I believe Indonesia (very small scale only) and the Middle East (have seen mentions but not anything too concrete)...
I think the first step isn’t thinking about something grand like aerofarms or similar projects... using hydroponics/aquaponics to control water use and environment management should be the priority, forget using LED for the moment, green house with sun light would work just fine... then would be automation of seeding, placement of crops into system and harvesting would already go a long way... We can figure the rest out later, for example, there was some proposal of using fibre-optics to channel light instead of directly using LEDs, and other such ideas to lower cost of a potential system...
The problem is the ROI of these types of projects as grains takes more time and the return per harvest makes it an unattractive enterprise... and I think the Chinese gov should take a bigger step in this... have some areas that might not be ideal for those grains and try different methods in a controlled environment... so that food supply especially rice is not at the mercy of the Yangtze River, like it is now...
For reference aerofarms