alt Hacker NewsThere are some routers with OEM fork of OpenWRT that allow you to flash stock openwrt without any obstacles and by easily dropping the image blob in the web UI - just easy as upgrading the firmware from stock openwrt.
Granted, not exactly what you wished for, but pretty close.
The time to do this is <5 minutes. One such router I personally know of is GL.iNet GL-MT6000: https://openwrt.org/toh/gl.inet/gl-mt6000
I use a GL.inet travel router and their UI on top of OpenWRT is actually pretty good and makes connecting to strange hotel and other captive portal networks pretty straightforward. Luci is still available, or SSH.
The OpenWRT version is relatively old, and unfortunately the latest firmware requires reconfiguring family permissions, but I’ve otherwise been happy with the device. I use it for all kind of strange things (ad-hoc extending my home network for getting my solar inverter back online, tethering to my phone, etc.), but primarily use it to make it easy to get my family’s devices online while traveling (6 iPads, 3 phones, and a laptop).