I don't see how my suggested system would be too complicated to manage. Could you elaborate on what would make it so hard? Each tile could be labeled with a code like "AA12", "CB50" and so on, so any plot would be easy enough to define just by listing the labels of the included tiles.

The biggest problems with predefined plots are that
1) there will inevitably be much unnecessary space on some plots that the mappers workign on them have no interest in, but which may end up being unavailable to other people for a very long time,
2) a mapper might want to work on a particular geographic feature (an island, a mountain chain, an isthmus, etc) that spans across the borders of multiple plots, meaning that they'll have to either grab all of those plots (assuming that's even allowed) or else work on them one at a time and hope that no one else decides to touch this geographic feature in the mean time. Worse yet, if predefined buffer zones are in place, it would be totally impossible for someone to map a geographic feature that happens to be situated in the buffer area.