Very dumb idea
Having worked for years in manufacturing CE/IT goods in the Far East - this is a really, really dumb idea.
I would be willing to bet there will be bona-fide product out there that some enterprising Chinese contract manufacturer has thought "I can save some money using these "local" FTDI chips". The company with responsibility for the product will have no option but to ship them back and replace the IC's - and this may not even be economical if the products have been potted or coated for harsh environment.
A pop-up message alerting the end-user to the status of their kit - or at the very least, if you brick the devices from working with the mainline driver, provide as a good-will gesture a driver which does work, but makes the user very aware they are using a knockoff.
In many cases FTDI chips will have been used as they are highly regarded over their counterparts (I've specified them on my designs in the past for this reason). I won't be using them in my new designs as a result of this action.
Biting the hand that feeds IT
