If they came out with one that retained all of the capabilities of the current system (IOW retained the AWD/center diff capability) I would pay up to $1500 for such a conversion. Seriously.
Can't remember if it was someone here or someone at
Home - ExPo: Adventure and Overland Travel Enthusiasts that actually replaced the T-case in a 4runner with an FJC case modified with twin stick (one for 2wd/4wd and one for Hi/lo.) He had the sticks come up through where the 12v outlet and smoker's kit come up.
I think if I ever had the dreaded electronic T-case failure, I'd be tempted to go with such a swap, especially if I was already looking at a ~$3k repair bill.
Of course, the only problem with that arrangement is that you lose the center diff and you basically have a conventional 4wd vehicle.
Last time I saw the Torsen Center Differential is non-electrical, so its "torque sensing" ability is mechanical in nature (its actually a planetary gearset). Now CDL is electrical but I believe (and I could be wrong as I haven't checked in a while) it is also managed by the shift fork assembly from the main actuator.
While a manual cable/linkage system could be fabricated, the main reason there's an electric system is mainly due to synchronization and ease of shifting. Now I'd have to have a transfercase apart to play with its guts, but I would assume even with syncros that any manual version would be a bit more difficult to shift into and out of 4WD modes.
The V6 would provide an additional challenge in that you need a secondary linkage that is either an entirely separate lever or somehow linked with the main assembly to actuate the ADD on the front axle. Now you could just eliminate the option of 2WD like the V8's and have the front axle constantly locked for a Full-Time 4WD effect like many do already (another option may be to eliminate the ADD and utilize old-school locking hubs in the front somehow,) but this is a design issue that needs to be addressed as well. There are also considerations to make in regards to leaving the front axles always engaged, while not as annoying or detrimental to driving manners as older Domestic 4WD systems, it does seem the V6 front axle does experience some minor bind-up when engaged in 4Hi vs. the V8's plain from clamshell (I also believe the V8 Clamshell in front is larger than its V6 brethren.)
The other issue is a matter of how you're going to control functions such as 2WD-4Hi-4Lo-4Lo CDL (if possible), this would require fabricating an entire shifter assembly that not only is compact enough, but bolts to the shift forks in the transfercase (the shift rods are actually part of the actuator and thus this hypothetical kit would require new shift rods that mate properly with the internal shift forks.) This of course brings me to another issue, whether you install this manual kit by using the old shift forks with new shift rods, or replace them with a new set-up (i.e. a new shift fork/shift rod assembly that allows servicing the shifter assembly without removal of the transfer case as is with the current actuator system), you still need to drop the transfercase and tear it down to properly install said kit, which would cost you additionally ontop of the actuator.
You'd also possibly lose/corrupt many of the ABS/VSC/TRAC functions that combine with the 4WD system to make it more capable that it is by itself due the the 4WD module needing to be disabled and the vehicle no longer being able to differentiate the difference between which 4WD setting it is in. Granted many people don't bother with the above assistance, but this could also result in aggressive over compensation from the ABS/VSC/TRAC system when you don't want it and would require you to disable most of those systems, which is difficult as it is heavily intertwined with the Hydraboost braking system used for your brakes and thus basic ABS/VSC functions remain even when doing "VSC OFF" mods because of fail safe coding.
As you shift into progressively lower gears in 4WD the system is aware of this and compensates with increasing its ability to assist. i.e. 4Lo, CDL On, Lo Gear nets you the most grip and even kicks in the ATRAC system to mimic a semblance of lockers in front and rear, this can be useful when you have 1 wheel in the air or are in very difficult terrain. Granted, many people rarely if every need to use these functions, but they work to subtly improve (typically, not always) the 4WD capability of the 120/150 Platform and thus using an add-on manual shifting system would possibly necessitate the installation of locker(s) to compensate for a loss of electronic assistance.
There are many design considerations to make and while I am sure it can be done (I'm seeing in my head little reason why it wouldn't work should the above larger concerns be engineered properly) it will end up costing you parts + labor to re-fit the existing transfercase. Thus no matter what you do, you still need to foot the bill to have the transfercase removed, torn-down, and then rebuilt (in the case of adding this manual linkage system, you'll need to find a shop that is willing to do the work; some may not due to liability reasons) so you're looking at an expensive modification/repair either way. You might just be better off getting an aftermarket transfercase or even trying to adapt an FJ cruiser manual transfercase (which may be easier to be honest.)
