Perhaps the people interested in the non-S upgrade a lot more, but due to this really complicated way of buying with pre-ordering and waiting for months, most of them just don't have the nerve to wait.
If 20-30 kits are build and list on ebay or aliexpress, perhaps will be sold in bigger quantities if that is the main concern for Javi.
I have already bought a display and want to know if that was waste of time and money.
Nothing to do with nerve. It's about the work involved and other things demanding attention.
Also, 20-30 kits is a drop in the bucket. If someone is willing to set up and front an order for like say.... 500 kits, I'm sure Javi would be more inclined to pick up and rush work on it.
These type of kits and upgrades, will likely stay focused for the chinese domestic market. There's enough business on the 51nb forums alone to keep them busy. The creators have no reason to deal with english-speakers on aliexpress or ebay, most of whom need their hands held each step of the upgrade process and the risk of a chargeback.