I think you're probably half-right. But the 4Runner's N280, while not the same as the J150, is close enough to consider them the same--and Toyota is not neglecting the J150/N280, wishing it will die. On the contrary, I think what we see is that Toyota is leaving well enough alone.
Not really. Prado is sold in more global markets and Toyota HQ has felt like there is significant overlap between Highlander and 4Runner in North America, and thus, 4Runner is not really necessary. Prado/LC150 is sold in higher volume worldwide, I believe, and also shares more direct parts with the cash cow Lexus GX. 4Runner is based on the same platform, of course, but is more differentiated ($$ to produce).
Of all the 4Runner generations, 5th gen is probably the most interesting to me when you look at the product decisions and lifecycle. Why? 5th gen is really just a stylistic update of the 4th gen but they simplified the product line by eliminating the V8 and just offering one V6.
There was originally a plan for a more substantial (expensive) mid-life refresh with a new 6AT, but that was tabled in ~2010 because of the economic collapse, falling SUV sales and rising gas prices. This is where Toyota started to say, "Maybe this is the last 4Runner," so they skimped out on the refresh and plans for a 6th gen were paused. This is where Toyota doubled down on the thought that Highlander is enough coverage for the midsize SUV market and 4Runner is an expense they can cut.
The 5th gen refresh shows up in 2013 and is very minimal with only stylistic changes, but by this time, SUV sales have not only rebounded but started going wild. Thankfully for Toyota, the 4Runner is seen as a reliable, familiar name and with so many crossovers hitting the market, it starts to look unique and "cool" as a BOF SUV and sales skyrocket.
At some point around 2015-2016, with such sustained strong sales and market conditions, Toyota decides to recommit to several BOF products that were hanging in the balance (budget, resources), like Tundra and 4Runner, and the plan for a scaleable TNGA body-on-frame platform becomes a viable business case. Seeing this is such a late development timeline, full redesigns for Tundra, Land Cruiser, Sequoia and 4Runner are all pushed back, we get new refreshes for Tundra and Land Cruiser, and the "new" Tacoma is just a refresh of the old one.
With this new timeline, Toyota plans a second refresh for the 2020 4Runner sometime around 2017, focusing safety systems and infotainment that will update the 4Runner again and hold it over until the 2022 redesign. At this time, there is interest and commitment for a 6th gen 4Runner.
In some ways, the 4Runner has beat Japan's own attempts to send it off into the sunset thanks to strong market conditions and consumer interest, but it has not been for a lack of Japan trying to consolidate product lines. Now that we will have cost sharing among all BOF products, it becomes easier to make the case for a 4Runner.
In full disclosure, I used to work with a guy who was Toyota's product marketing manager over the 4Runner, FJ Cruiser and Tacoma, so I have a bit more historical context that I can't share in full detail. But yeah, there's your story.