I don't know, given how poor the MPG is on the new GX, that tried and true V6 on the 5th might remain desirable. That's kind of why I'm thinking it has to be the V4 hybrid.
There's a lot of ways for Toyota to go with the new 4R. But it's almost certainly going to be the turbo 4cyl 2.4L engine. The main reason is EPA ratings both for emissions and for mpg. The turbo engines perform around 20% better in the EPA test. Not as much in real life.
I had assumed the v6 was dead at Toyota - but the new Lexus TX continues with a 2GR and hybrid combo. Not sure why, but TBH it's probably a fantastic combo. Smooth, quiet, super reliable, low maintenance. And the 1GR continues in the LC300. The reports from people who have driven the GRJ300 say that it's a completely different experience with the 8 speed transmission (or 10? I can't remember which it has.) Lots of positive reviews. Some say it's better to drive than the 4.6L v8 in the LC200.
However, the emissions is the issue and I think it'll be the T2.4. In a long form interview with the engineer head of that engine design they discussed how different it is from the car version. Apparently it is significantly changed for the truck version and the truck version requires a substantially higher durability test and about 30% longer expected service life vs the car version. They also do different testing on the truck engine - tilting it to what sounds like the most extreme angles the truck can handle - I think meaning the roll over angles and then run it at max heat load which is less than redline until the turbos turn to red and then to white in color and then they rapidly cool them (water quench??). Lots of very heavy durability testing for the truck engine that isn't done for the car version and make changes as necessary. The claim was that roughly 1/3 of the engine parts are new for the truck version vs the car version. And the truck version has better power and performance on 87 octane than the car version does on 91. (So why not apply the same changes to the car?).
The other 2 interesting comments were that he said that they intentionally engineered hand room and work space into the engine bay so you can work on it with normal tools and maintain and repair it. He also said that they had a metric for the Tacoma design from day 1 that included a driveability factor and that apparently they didn't have that in the last tacoma. So, in the last taco design the powertrain groups were somewhat silo'd apart and at the end then had an engine, transmission, and vehicle that didn't fit well together and made for the poor driveability we all hate about the current Tacoma. How Toyota didn't consider that is remarkable to me. But, apparently that was a base design metric this time and a lot more effort was spent on matching the engine power, efficiency, balance/smoothness, and truck power needs so it doesn't constantly hunt for gears and always feel so underpowered. We'll see... I'm skeptical that the little 4cyl will be enough for a 5k lb SUV. I'm even more skeptical that it would be adequate for a near 6k lb LC250, so I'd be a little surprised to see it in a new Land Cruiser.
Anyway - the general takeaway is that the T24A for the truck models including the new 4Runner most likely, is expected by the design group to be as durable as the outgoing 1GR and to have the same service life. And it has a bunch of internal changes from the car version.
Time will tell if it's a winner. But I'd bet that it's the only engine option and it comes with and without hybrid options plus a possible PHEV model.