Yes, built-in WiFi is always on our todo list. But keep in mind that having built-in WiFi will probably raise the price by $40-50 due to the hardware and development costs. Currently using an external WiFi adapter is still a cost-effective solution. The TP-link WIFi adapter that we recommend is less than $20; and if WiFi signal is an issue, you can use the TP-link Powerline adapter, which is about $30 and requires no configuration at all.
At the moment we are recommending either powerline adapters or the TP-LINK WiFi adapter. I agree that build-in WiFi would be a better solution, but it’s not really cost-effective. The TP-LINk adapter is $20 and powerline adapter is $30. These are not that more expensive than USB WiFi dongles. Also, powerline adapters are more reliable and less prone to WiFi signal issues.
As another part of the added cost: having built-in WiFi means the product needs to be FCC certified (OpenSprinkler is FCC verified, and does not require certification because it doesn’t have intentional radiators). Having intentional radiators means we must test the product to acquire an FCC ID, even if the circuit is made of all FCC-approved parts.