Man this thread has been an entertaining way to burn some time at work. Here's my take, which is worth less than a virtual grain of salt.
I feel like it's pretty obvious at this point what Toyota's plan is. We're getting the light-duty J150 successor branded as the "Land Cruiser" for US marketing purposes. To the majority of US consumers, they don't know s*** (or care) about J-designations or whether-or-not the "new Land Cruiser" is a true successor to the outgoing station wagon. They've done this in various markets already - nothing new.
It should come as no surprise that US marketing shows 40s, 60s, 200s along with the new J250 - those are the "Land Cruiser" widgets (to use my favorite
@OGBeno term) that the US market knows and associates with the US "Land Cruiser" brand. It would be pretty strange if they showed a Toyota-badged J150 Prado that we never received here as the outgoing model in marketing material...
This is a US market release of the US-market "Land Cruiser" - it is not a global release, or a Japanese release, or an Australian release. Sure - those of us that know the J-designations and the underpinnings of the J-series trucks will be watching from other markets to get a glimpse of what they will likely receive as their "Land Cruiser Prado". We will see during those releases if they choose to drop the Prado name (like the 70 having the same "Land Cruiser" badge as the wagons), give it a new name, or just keep it the Prado. I bet you will see them marketing the "Prado" badge harder in those releases just like they did with the J150 releases in those markets.
Physical size comparisons between the J250 and J300 are not the only thing that matter. Spend some time under each truck, or just keyboard jockey some google searches, and you will quickly see the difference in almost all drivetrain components. Thinking the J250 is going to replace or be an equivalent to the J300 is silly.
Obviously what's going to happen with the 4Runner is the largest unknown, but honestly that seems to be clearing up with each announcement as well. It makes no sense for them to drop the 4Runner brand, it's worth too much and it was born out of the US market. My gut feeling and what makes the most sense from a line-up perspective will be for the 4Runner to shrink in size slightly (or remain the same-ish since the J250 is larger then the 4Runner-sized J150) and have all the same (smaller) engines that were announced with the Tacoma. I know they have done it before, but it just doesn't make much sense to me to have two trucks (J250 & new 4R) be exactly the same size. If they are the same size then the 4R will probably get very distinguishing features like the FJ Cruiser did (which was also a J-designation). So from smallest-to-largest you'd be looking at 4Runner/Tacoma -> J250 "Land Cruiser"/GX500 -> Sequoia/Tundra.
but once again - I couldn't be less qualified to assert that any of this will come to fruition, but its a fun mental exercise none-the-less.