I think the 100-series will last atleast as long as the 80s have, there are several improvements over the 80. The front axle, which on the 80 is a constant worry, are the knuckles leaking, will they be leaking tomorrow? With the 100 it's all IFS with sealed rubber boots, which as far as durability is a much better design, with the sealed rubber boot full of grease, the grease can't go anywhere, the joint never leaks, etc. Ofcourse there is the issue of whether you like IFS over live axle, but we're just talking durability here.
I don't understand where this notion that a V8 is any less of a quality engine than a I6 comes from. There have been millions of V8s over the years, just because this is the first Toyota has made means nothing...no, actually it means that they took what they learned from making millions of I4s and I6s and put those same ideas into a V8, which is arguably better than any other V8 made to that point. Part of the 'lore' of the I6 is not just that it runs forever, but it has lots of torque and therefore is easy to drive, good 'offroad' engine, that's neat but being a good 'offroad' engine does not make it last any longer.
The 4.7L is the exact same Lexus V8 put in the LS400s (family sedan), only with a taller deck height, longer stroke, more displacement, many of those cars are well over 200K miles and never had a problem. The LS400's are one of the nicest, oldest cars you can buy that still are wonderful cars, even with hundreds of thousands of miles on them.
Rarely is the engine the limiting factor in any vehicle though, almost all Honda cars made will run to over 200K miles, but most don't because the owner gives up on them, or something small goes out (alternator, water pump, etc) and they dump the car. Even cheap cars, like a Ford Escort, I've had 3, all ran to 170K+ miles, never a problem, and I sold or gave them all away and everyone was still running fine. So the engine is hardly the question in my book. I think the interior is a very good estimate of how the vehicles will last.
Compare a '98 Cruiser to a '98 Durango (did they have them in '98?), or a '98 Explorer, even from normal wear and tear, the Cruiser fares much better, higher quality materials, more sound proofing, etc. That is what makes the vehicle last in the public's eyes. You can have a drivetrain that will run forever but if the interior is shot, paint peeling, nobody will drive it and the vehicle has effectively not lasted as long.
On the other hand you have the 100 series, quality built vehicles which many are well over 100K miles, in only a few years, look/feel/drive great, not like a 6 yr old vehicle with 100K+ miles, but like something new.
I'll buy a 100-series just as soon as my 80 wears out, and damnit it hasn't yet!
Just my $0.00 worth...
Mark Brodis