A 6AT would make a pretty noticeable difference, I think. Floor the 5th Gen 4Runner at 70 MPH and it really only downshifts from 5th to 4th and there's quite a wait for usable power to show up. Another gear and shorter ratios would be nicer for passing, towing, higher elevations and gas mileage.
Toyota has very rigorous testing processes for the parts that are used in the 4Runner, Tacoma and Land Cruiser (and derivatives) - they undergo more stringent testing, more abuse and more miles than other vehicles in the ToMoCo lineup. These are some of the very best built vehicles available in the Toyota family, and the company takes reliability, dependability and capability
very seriously. This is often why it takes longer for new technology to make it to these platforms. It's also why they last forever.(
this is a good article to read if you're curious.)
With that said, Toyota
does have an 8AT that's about to be connected to both the 5.7L and 4.6L V8s. Whether or not that transmission is an easy/suitable bolt-up for a V6, I am not sure.
After losing the V8 from the Gen 4, and then about ~300lbs of weight added to the Gen 5, Toyota received a lot of complaints from 4Runner owners who wanted to tow more or just generally felt like the truck was underpowered. As I understand it, there was some consideration of putting the 1UR-FE 4.6L V8 under the hood as an option for the 2014 refresh, but this was a topic of debate when the price of gas over $3.50 in most of the country. Ultimately the idea was dropped.
The 4Runner is almost a victim of it's own success, and I don't think Toyota ever assumed that this generation would be as successful as it's been. It bowed right after the financial collapse, gas skyrocketed, crossovers boomed and almost every other BOF SUV went extinct. Somehow, the 4Runner soldiers on and has actually been increasing sales volume year over year except for a slight dip between 2010 and 2011. As mentioned before, I know that about 2 years ago, Toyota had not even committed to build a 6th generation. I have to believe that with such unexpected success, Toyota is definitely committed to another generation at this point.
The question is just how much they're willing to invest. Are we going to get a full redesign with new everything? I doubt it. I think it's more feasible that they'll nip and tuck the exterior, modernize the interior and make some small upgrades to the power train - possibly a beefed up version of the Tacoma's new V6 or maybe just bolting a newer transmission to the existing engine.
Good news is that I think we should know more in the next 8-10 months, but that is a long wait!