[1] https://iopscience.iop.org/article/10.1088/1757-899X/678/1/0...
the current max is 1600C with cooled monocrystal blades. The 1800C seems to be a worthy goal post in this situation. More advanced cooling and/or say some tungsten composite for example. Even if they end up with "just" 1700C it would still be great.
Wrt. 6th gen in general - it looks what everybody is doing is just targeting the goal posts just a bit behind the 5th (some are even basically skipping the 5th). That actually would give us the 5+th gen. The true 6th will have totally new capabilities plus of course all this advanced 5+th tech as a base. Currently it seems to me that autonomous/AI will be that new capability (on top of much improved engines, radar/sensors, stealth body). This will also as usually differentiate top players possessing the next gen capabilities from the rest wannabes.
At Mach3 the SR-71 airframe got to just under 500c at the hotspots.
The reentry temperature of the space shuttle peaked at around 1600c.
1.6-1.7K is the temperature of modern afterburners so if 1800c/k is a figure of anything it would be that.
That said the turbine entry temperature for modern jet engines is about 800c so maybe the 1 was a typo.
An sacrificial ablative coating which survives 1800C° is different from a turbine spinning 25000RPM doing the same for thousands of hours.