At the current stage, two engines are considered. V8 High Performance Turbo in F-Sport to compete with MB AMG. Displacement is less than 5.5l.
2.5l inline 4 “downsizing turbo” with 10-speed auto from Aisin. This transmission is both highly efficient and with high performance.
A Lexus LS 250t is not inconceivable — after all, BMW will offer their new 7-series as a 2.0L four-cylinder hybrid and Mercedes has S 300 Hybrid, which is powered by a four-cylinder twin-turbo hybrid engine.
(I’ve always thought the LS should have a range of engines, but would have expected a V6 option before a four-cylinder turbo. That said, a LS 250t would be built for China and similar markets with high taxes on high displacement engines.)