If Texas built is truly better designed, they would start by buidling MYP and keep Fremont building MYLR until volume is ramped up enough to upgrade the Fremont facility.
I would think it would make more sense to move the highest-volume car to Texas first (MYLR)... that would provide the most relief for Fremont for factory retooling/upgrading. Fremont could even use their freed up capacity to build a ton of current style MYPs in advance of the shutdown to minimize customer disruptions.