Eh... alright I'll play [MENTION=66316]1engineer[/MENTION].
~4Cyl Turbo Diesel Option (Unlikely unless the Diesel "revolution" picks up enough that its worth the effort for Toyota to meet the ridiculous standards the US wants to push for Diesels as well as training & parts)
~A standard 6Cyl (I feel a 4cyl, even with forced induction is just not robust enough for the demands of towing/off-roading, otherwise we'd see it in F150
s and GMC 1500's,) Supercharged engine (the 1GR-FE while a good engine, needs better low-end, something a Supercharger will do better than a turbo charger), possible with GDI (again unlikely as the DS4 system is not a true GDI set-up and Toyota seems to be a bit adverse to GDIs, for understandable reasons in terms of reliability and servicability), with Dual VVTi (for the love of god don't let them put that craptastic "ValveMatic" BMW knock-off BS in it!)
~Possibly even a high efficiency V8 (many of the F150 guys who got suckered into a "EcoBoost V6 you can't tell its not a V8" regret buying that engine as you really can tell) which could be achievable with current technology (i.e. GDI, Dual VVTi, ect.) while providing low end torque and good fuel economy (this would probably end up being an optional "mid-level" engine on the Tundra such as the 1UR-FE 4.6L is currently)
~I would like to note that a hybrid option is just a horrible idea and is not something you want on a vehicle you're depending on out in the middle of no where. I don't feel hybrid technology nor electric vehicle technology has come far enough to really warrant it being on the trails yet (mainly in terms of reliability, cost effectiveness, environmental effectiveness, infrastructure, ect.) Maybe in 15-20 years when the US infrastructure has hopefully caught up enough to actually support a decent amount of electric vehicles and they are reliable enough to stand up to the abuses seen off-road, not to mention find a way to make them easy to work on in the field, then it might be a good idea.
~Actually come to think of it, a smaller INLINE 6cyl (possibly with a supercharger) might not be a bad idea as they tend to be a bit more torquey than their banked brethren...
~Drivetrain ideally would blend the civility of on-road handling with off-road capability. I feel the transfer-case setup from the 4th gens with their Torsen T3 center differential provided the best blending of these two worlds by letting the 4Runner operate in "grey" areas where a part time 4WD system has to be either on or off and this results in that sloppy Domestic 4WD feeling. With the 4th gen I found it did a great job at this transition, as was stated many owners just drive in 4Hi on their 4th gens because the vehicle is so capable off-road and civil on road in that mode.
~A 6-Speed Automatic transmission would be best for the 4Runner, perhaps a 7-speed IF they could get the gearing and software mapping correct so it doesn't feel poorly geared and/or hunting for gears constantly under light load (i.e a small trailer or extra weight in the vehicle.)
~I'm a bit hesitant about an Aluminum frame, particularly for off-road use as that makes me be a bit paranoid; but if Ford manages to pull it off, that may not be a bad idea. I do think some reinforcement with CERP like BMW is doing with their i3 & i8 would not be a bad idea for the body of the 4Runner. BMW is getting CERP manufacturing down very well and Toyota may as well take advantage of their horrid partnership with BMW by figuring out how to apply it to their vehicles. But bottom line it needs to remain BOF to retain capability. Unless Toyota can somehow invent a Unibody that can actually flex reliably without cracking/tweaking and still keep all the panels lined up (doubtful.)
~The shape should be an evolution of the 5th gen, I feel the angular features of the 5th gen feel most like a 4Runner and a natural progression of the 2nd & 3rd gens (I like my 4th gen, but only with armor and such, stock it's too soft.) But for the love of god they need to do something about the interior ergonomics. It looks nice, but the 5th gen is just awkward and uncomfortable compared to my 4th gen, everything feels either "just a little bit off" or "a little to far to reach for." A good study of what worked well in the 4th gen as well as other SUVs and a good evolution of the current interior's appearance would result in a great modern, off-road feeling, yet comfortable interior.
~I would like to see some rubberized flooring for the 4Runner (also the Tacoma and Tundra) as these are supposed to be advertised as either work vehicles and/or off-road vehicles. Toyota did a nice job with the FJ Cruiser and I feel they could work it into one or two "Sport/Trail" trims to differentiate the people who want leather and the people who want their off-road 4Runner.
~Retaining the current IFS suspension is not a big deal to me, I find the IFS to be adequate for most off-road excursions and to provide a good balance of civility and capability; though an update/evolution of the current short arm/long arm double wishbone may be in order to better enhance capability (clearance, articulation, ect.) while providing civility (I know they can do it)
~ I would however strongly recommend they retain the solid rear axle, going to a RIS I feel would greatly hamper the capability of the 4Runner as its meant to actually handle obstacles as well. If it were mainly for desert running I wouldn't be opposed, but I really can't see as much benefit in a RIS without severe engineering (and thus extra cost that Toyota would likely not pursue) to make it as capable as the rear solid axle.
~Their reliance on the ABS system for features such as ATRAC and such is commendable and for the last 10 years has served them pretty damn well. I would say further fine tuning and software options (terrain selection, manual VSC/TRAC disables, ect.) would be a good idea as well.
I'm not sure what else I can think of at the moment on top of this list, but I'm sure there's some other things.