That falls apart as soon as the author with the locked paragraph leaves the document open while they’re doing something else, preventing others from editing.
I really don't get it. You want to add thousands of lines of code and complex data structures with tons of edge cases so that I can interrupt you while you write??? It's just not desired functionality. Poor network connectivity is not an excuse to break your workflow.
You simply do not assign 2 people to a task that can only be done by a single person.
It is like a system where 2 people can poor coffee into the same cup at the same time. We deal with the cup overflowing with some drainage (marvel at our creation of course!) but then 12 people put sugar in the cup. Solution: we overflow the cup further to dilute it! We solve the mobility issue by spilling a bit more coffee out of the cup and whip the bottom with just the right type of towel or napkin. The only problem that remains is both drinking from it at the same time.