If there’s an active Ethernet connection into the “WAN” port it will use it all the time. But there’s times I don’t want to use it (i.e, when I’m in hotels sometimes) and would prefer to not have to manually disconnect it- it would be so nice to have a “Disconnect” button for the Ethernet WAN, just like with Cellular (for my X3000), Tethering, etc.
RN I fake it by using an Asix-based USB Ethernet, so it shows up as “Tethering”, but that’s such a workaround.
… please, guys?
Nah, that’s nothing you really need. That’s not how WAN works.
If you want to disconnect, you can simply pull the cable or disable the interface in luci
… says who?!
Cellular is a WAN. Has a “DIsconnect” button
Tethering is a WAN. Has a “Disconnect” button
Says me as an network admin since a few years.
Cellular + Tethering are both different because they are more an “application” than a wired connection. As I wrote before you can disable the interface if you like to. But using a router which is connected by wire and then wanting that it does not connect by wire is pretty … weird.
Why does it matter how you get to the general Internet? WAN is WAN. If there’s a way to do it via LuCi, then why did they wire up buttons for Cellular and Tethering? After all, they’re just “EthX” interfaces too in the UI
Because it’s not useful for most of the users? Since you can enable / disable it via luci anyway, what keeps you from doing it there? 
Or, if you prefer scripting, you can use ssh