4wd problems

The viscous coupling would simply provide the means to reliably use 4wd in changng conditions. You would still use 2wd for the vast majority of the time, so reduced fuel economy and wear on the coupling wouldn't really come into it
The viscous couplings themselves are just a small block that would be integrated into the front prop so there's no significant weight gain or added complexity. If it did lock up then you'd be back to standard Jimny 4wd operation.
Anyway, it's just an idea I had. I might make one someday if I come across the right ingredients.

Re the Stalwart comment..yep wind up was a proper danger, I saw a lad thrown across the vehicle park after he jacked up one side to change a wheel ....he had been told to bounce it off the kerb first but thought he was being initiated as he was new to the sqn ..He learned though. Now that was a go anywhere vehicle !

You have a point, Less is sometimes better (mostly in my experience).

Series landies , if memory serves me also used to strip half shaft splines regular as clockwork. I think they changed the splines more than once to try to cure it.
As for Rogers comment about drivers abusing their mounts, I thought that was Standard practice for landies back then. If the condition of S/H landies back in the day was anything to go by it must have been mandatory.

Re viscous couplings, The idea certainly has merit. Could wind still up be a potential problem if you were say pulling hard uphill on a bend? The coupling still has an element of drag as far as I am aware. A bit of caution may still be required?

Agreed, its not actually a problem, Just a bit of a pain having that extra stuff to think about. I was just posing an idea that would make driving simpler without losing the benefit of 4wd.
Torque biasing diffs or limited slip diffs have the benefit of improving traction without any input from the driver. They are a relatively simple mechanism wholly within the axle casing with no external parts required. Whilst allowing normal driving. If used in a centre diff, windup would be a thing of the past unless you were seriously abusing it. In which case you would probably go for diff locks anyway or choose a motor without a centre diff.
All with NO electronics to fail.

The viscous coupling would definitely allow enough slip to avoid any windup. That is precisely why they are used in the applications they are. An AWD vehicle with a viscous coupling essentiually behaves as a 2wd vehicle until that axle loses traction.
For a serious off-road use it would be detrimental but for the vast majority of Jimny users it would be a massve benefit.