Pardon my total ignorance but why would one invest in Nautilus when you can buy for the same price Yamaha MODX6 + Cubase Pro + Absolute 4 with 6,800 presets and more than 100 GB library.
Not everyone wants to work with a computer. It can be inconvenient for gigging, or if your computer and keyboard aren't typically located near each other, or you don't want to deal with some of the initial complications or don't like the general workflow... Also, does that necessarily give you everything the hardware does? Can you seamlessly switch from any combination of up to 16 sounds to any other combination of up to 16 sounds? (And I don't think Absolute includes all the modeling and other synth engines of the Nautilus, though one could buy additional VSTs that should be comparable.) Also unknown, is the action comparable? (OTOH, if you are happy with the computer approach, you can arguably get by with a lesser board than the MODX6!)
What is then Korg Nautilus target customer?
At the moment, I think people who find the Kronos appealing but wished for a lightweight non-hammer 73, or are intimidated by the busy front panel of the Kronos, or who feel they don't need the extra Kronos advantages and would rather save a few bucks. Or maybe even people who are scared off by KARMA and wish it has a simpler arpeggiator based system instead. In the long run, I don't think this relatively small price difference between Nautilus and something higher end will be maintained, so... ask me again a few months from now. ;-)
As for the car analogies above, this is something I posted elsewhere in 2017, which still largely holds, I think...
Casio = Hyundai/Kia. High value, with a quality reputation that has grown beyond its budget beginnings.
Hammond = Jeep. Anything else is just an SUV.
Kawai = Volkswagen. Fahrvergnügen.
Korg = Ford. Models for every niche, with occasional adventurous designs.
Kurzweil = Mini Cooper. Repackages the same basic thing a dozen different ways, but its fans love it anyway.
Moog = Tesla. What everyone wants, but few have.
Nord = Volvo. No-nonsense, premium designs without unnecessary frills.
Numa/Studiologic/Fatar = Fiat. On paper, they look great. When they hit the streets, sometimes they work, sometimes they don't.
Roland = Nissan. A mix of super cool with "what were they thinking?"
Yamaha = BMW. Solid top of the line products with interfaces that can drive you crazy.