My hunch - and pure speculation - is that these will be two new engines for Toyota/Lexus.
They could drop the same old 2.5L 2AR-FE in there, currently working in the Camry, Rav4 and other applications, but that engine is getting older. As Toyota/Lexus move to Atkinson/Otto cycle and D4-S technology across the board, I'm betting we see a new 2.5L 4 cylinder very soon.
Toyota has a new 2.0L 4 cylinder used in Asian markets that has Otto/Atkinson, D4-S and produces 165hp. I assume we will see a slightly larger, slightly more powerful version as the next "workhorse" 4 cylinder in Camry, Rav4 and most likely this UX. In current 2.0L form, that engine breaks out to be 82.5hp/L, so I think it's very reasonable to think a 2.5L version (with the same tech) would ring in around 200hp (206hp exactly, based on my prior calculation).
The "250h" model is most interesting. I know I'm being very speculative here, but I assume that a new hybrid - 2.0L four cylinder + next gen hybrid batteries - to give a "2.5L-like" output around 210-215hp.
As the current "300h" system used in the ES 300h and NX 300h is getting older, this would give Lexus a new "in-between" hybrid option that slots above the Prius/CT's 1.8L hybrid but below a possible next generation "300h" option for IS, GS, RC, NX.
I'll go one step further to say that if Lexus was to combine that new, hypothetical 2.5L 4 cylinder above with a next-gen hybrid, you get a ~240-250hp "300h" option, which would be a great upgrade.
All speculation, but fun to think about. I bet I'm not too far off, but we'll see.