Structure-aware: if one change sets a TODO item to WIP, and another to DONE, a structure-aware merge algorithm could resolve this conflict, e.g. based on time; plain git needs human attention.

Well, yes, immediate sync should work, all merges would be fast-forward except for a vanishingly rare case of two conflicting simultaneous pushes.

It's not very practical if one of the devices is mobile, so it's not always online, and parallel changes may build up sometimes.