Background
Me and some friends have been playing Minecraft since around 1.1, we started our current world at 1.2 which initially was SMP but we later moved it to SSP with LAN host.
Back in the days we were rather active and always upgraded to the newest version when it got released up until 1.8.8. That's when for various reasons our Minecraft sessions became less regular and we abandoned the world for a while.
When coming back 1.9 had released and we weren't too fond with the changes. Combined with not playing Minecraft as often any more we decided to no longer upgrade as we would have to check patch notes on every session.
Now several years have passed (5 in fact) and with the Nether Update out we're considering upgrading again.
The issue:
Our world houses a variety of farms to make obtaining items easier. Some of these including
- Sugar cane farm
- Mob farm using dispensers with water to push the mobs down
- Witch farm
- Zombie Pigman farm
- Enderman XP farm
- Item sorter
Furthermore we make extensive use of villager trading to get our gear and some resources.
Now my question is, what will break on the way from 1.8 to 1.16?
Keep in mind that I am talking about the Java Edition of Minecraft
I'm only looking for survival gameplay related changes. So back-end stuff like The Flattening and map making features like Structure Blocks should be ignored for answers.
I'm also NOT looking for information on what has been added throughout the updates. That information can be found by checking the version history on the Minecraft Wiki.
Best Answer
Let me try an answer more specific to your question:
The sugarcane farm will work, although it's massively overcomplicated and laggy comparing to modern alternatives. Consider building a new one before decommissioning this (or turning it into a museum piece).
Mob farm using dispensers with water to push the mobs down - works. Entity cramming won't allow accumulating mobs for occasional XP harvesting, and dispensers are more expensive than waterlogged trapdoors, so depending on your specific design it may be less optimal than what it could be. It's probable you may be able to 'upgrade' it to trapdoors and recover a ton of dispensers. Also depending on killing mechanics more optimal may be available.
Witch farm: this will break, the shifting floor mechanics have changed significantly several times, and a simple floor of slabs simply won't make the witches drop down. At the very least replacing the spawn floors with alternating solid blocks and soulsand, and open trapdoors over that, like in this one, although at that point rebuilding the whole thing would likely be little more work and improve your rates too.
This zombie pigman farm will work, but worse than before. It may require shooting zombie piglins from time to time to re-aggro them, adding means of disposing of magma cubes, piglins and hoglins, but in general it can serve as a framework for upgrading to an optimal 'donut style' zombie piglin farm; the worst, menial part of the work is done.
Endermen XP farm: Will work just fine, and produce exactly as much as before. If you're not saturating your XP intake though, you may consider building an EnderMINI instead, it's a cheap, maybe an hour build that works even better. (though if you're producing more XP than you can absorb with this one, the upgrade is meaningless).
Item sorter: Should work, most of it - the storing slices, water streams etc. There may be some issues in the 'quirky' parts like overflow etc, related to 1.16 redstone dust changes:
This usually doesn't render a contraption useless, just requires some tweaks and adjustments.