Just curious. Does a pre-production model to evaluate mean that the SX series is not finalized yet? And, how about all those posted videos by Yamaha, Peter Baartmans, and those from other countries, who seem to be showing a finished product? Might the model for the U.S. market be different in some ways?
There are a lot of "moving parts" in a product launch, not just development. The whole Yamaha marketing and distribution machine must be cranked up, manuals written, etc. Not to mention manufacturing set-up.
From the functional point of view, the SX is probably 95+ percent complete and is likely in final QA. Given a Fall 2019 release date, Yamaha may soon be initiating the first long production run in order to have product available in stores at final release.
That's my speculation, anyway, based on years of product development experience.
Hope this helps -- pj