The 3 trademarks have been filed in the United States as well. I wrote about that, with some additional engine commentary, in this
Kaizen Factor story:
http://kaizen-factor.com/toyota-trademarks-trio-uxs-lexus/
Probably,
if the Lexus UX is to be closer to Toyota C-HR engine-wise, as is the case with ES/Avalon, RX/Highlander and LX/U.S. Land Cruiser. If, on the other hand, there is to be more Lexus vs Toyota powertrain differentiation, as in NX vs RAV4 and GX vs 4Runner, then I'll agree with Krew's prediction of a
de facto 6AR-FSE (which may bear a different engine code). My article linked above addresses this in a little more detail, as well as discussing the two different Toyota 2-liter 4-cylinder engine families.