I first found this forum in 2002. At that point there were still very vigorous debates about the efficiency of full suspension bikes compared to hardtails and quite a few people considered disc brakes not worth the extra weight over rim brakes. 29ers were for weirdos who’d decided that singlespeeding was no longer niche enough for them.
Even then a modern enduro bike like my Nukeproof Mega 290 would probably have been met with bemusement. The enormous amount of travel for its weight and things like the shock damping and brakes would have impressed but I reckon the main impression would be “what do you need all of that for except for downhill racing?”
Go back another 10 years to the early ’90s and I think the reaction would be similar, but magnified. The technology would impress but the purpose of it all would confuse most. “Won’t it just steamroll over everything?” “Couldn’t it be lighter with less travel and still be more than good enough for what we ride?” “Wouldn’t you rather have some manoeuvrability instead of all that stability?” “Where do you put your water bottle?”
On the other hand I reckon that if you took a rider from the early ’90s into the present and showed them the sort of trails that are the natural environment for enduro bikes and the speeds they can be ridden on such trails and they’d be much more impressed.