YouTuber Nintendo Prime (first spotted by Video Games Chronicle) took the OLED Switch apart and found the dock has an HDMI 2.0- compliant port, suggesting there's 4K potential in the hardware - even though the Switch OLED itself doesn't support 4K output.
Previously, the Switch shipped with a HDMI 1.4 cable, displaying either 1080p at 60fps or 4K at 30fps, the latter of which was never incorporated.
The device also integrates an ARM-based chip, but the OLED Switch still is unable to display 4K output. It still uses the original Switch's Tegra X1 chip, which can't support 4K output.
The Switch OLED Dock Is Capable Of Supporting 4K, 60FPS
Some speculate that Nintendo is future-proofing the OLED Switch by incorporating these features, including Nintendo Prime.
This system is just going to run the same as far as we’re aware, you’re just going to get 1080p60 for the lifetime of Switch OLED. But, the dock with the 4K60 output could be reused in a future Switch revision that does do DLSS, and that would be handled on the system level, not the dock level.
Still, it's just speculation at this point. Nintendo officially denied 11 studios received 4K dev kits and asserted that no other Switch model is being developed. Any news of a new Switch model will likely wait until after the OLED launches and the holiday rush subsides.