It does, but it would be handy to know without entering the BIOS setup menu - like the LED on the Lotharek-stereo.
The fact the stereo state is reliably reported in the BIOS makes the LED redundant for me (and I don't like drilling holes in the case anyway), but if you're determined to have another visual indicator, I guess one of your suggested LED wiring solutions would work. U1MB provides no inherent signalling mechanism for XEGS mode. I think it was envisaged that one would fit the jumper when installing the device in an XEGS machine and then forget all about it, the pastel buttons being a strong visual indicator of the current mode.
Since the XL/XE lacks the XEGS's detachable keyboard, TRIG2 (keyboard sense) always reads $01. I think the XEGS OS only boots the game ROMs when the keyboard is disabled, so unless you hack the OS, I wonder if XEGS mode is much use at all on an XL/XE, let alone the ability to switch it on and off ad-hoc.
Edited by flashjazzcat, Thu Aug 18, 2016 9:45 AM.