I was able to get this to work on High Sierra by doing the above for BOTH Log Out <Your Name> and Log Out <Your Name>…. Weirdly enough, by default High Sierra shows just Log Out <Your Name>…. If you override this shortcut as described, another item appears in the "Apple" menu, this time without the ellipsis: Log Out <Your Name>, and having the same cmd_shift_q shortcut. Only when you override this second item can you truly free up cmd_shift_q.

@fingaz Thanks for your input. To be clear, I already have a free thunderbolt port-- I'm not sure why I would need to daisy chain. According to my above references, however, when both thunderbolts and the HDMI port are used simultaneously with three 4K monitors, only two of the monitors work (one of the thunderbolt monitors goes dark). I am wondering whether if I plug a non-4K third monitor into my open thunderbolt port I can expect it to function. Or is there some reason that daisy-chaining would work but not using the open port directly?

Everybody should look at @TedWise answer below, it explains why the list obtained through this method is not complete.