Yup, I just wrote an article [1] about just this. Simultaneous co-editing doesn't work unless the UX includes the appropriate cues to avoid this sort of thing. There are astoundingly few good examples of good (much less great!) real-time coediting UXes. This is the primary reason why we added first-class support for these cues so that it's not so damn hard!
Agreed. My first UX attempt was to simply put a list of the current editors on a document in the upper-right corner, and highlight the field or paragraph being edited by each person. It worked well enough, but this was also a limited scale audience - just a few dozen legal document authors. A larger scale app might require more, but it met the need we had.
Could you elaborate on the kind of bad UX you've encountered, and what solutions can be used to fix them? I can't think of anything that a simple cursor position indicator (and maybe a selection indicator - though that could get messy if the selection is large) doesn't solve.
[1] https://convergencelabs.com/blog/2017/09/what-makes-for-a-gr...