@humfrydog Sadly to make oceans spawn right and fix the mansion issue alone tell me a reset is best. We all saw the problem with mansions on a partial reset and the lack of totems available. F
Factor in fish will only spawn in certain regions there is potential for existing afk fish farms to have an advantage over new ones depending on if the fish are water biome specific. I also foresee half formed shipwrecks and half formed ruins like the mansions where old map meets new.
I know very little about coding so I claim no knowledge but I can see the Possibility of multiple issues past and present a new map would best address. again tho my opinion. i really am looking for to the new features, challenges and opportunities.
We always talk about no unfair advantage however players farther out will have just that as there will be less unexplored lands nearby whereas new players will need to travel long distances. So basically legacy players will get there first in the beginning and with better gear will dominate the new stuff. A map reset puts all equal. it sucks but i think would be best.
Reminder this is opinion and doesn't reflect anyone's attitude over a reset but mine.
If we did stay on this map for even longer, and into 1.13, the map would inevitably have a lot problems. I would expect biome problems, new players would just die after a few hours due to phantoms since beds currently mess up sethome so it would have to be changed, I would expect a lot of the command blocks would be messed up due to commands being changed, people's redstone contraptions and builds would be messed up due to new water mechanics, and of course a lot people would just not be happy (either way to be fair).
In my opinion a reset would be the best decision.