Again, I'm sorry if this has already been addressed as not possible, I don't think this has been talked about officially.
If it already has, you can neglect this and share where in the comments below.
Randomizer UHC 1.12+:
1) I'm going to start off simple. In Minecraft 1.12 there are several more blocks to go through as well as items, such as Purpur blocks and crops.
2) In 1.9+, the PvP was changed. Some like the new way of PvP, others don't. This is a sub-suggestion to go with this one. Make the new Randomizer UHC have 1.8 PvP with Enchanted Golden Apples enabled, since some chest drops have them.
3) Ever since the current 1.8 Randomizer UHC came out, some players were disappointed in not seeing any chest drops from blocks. So, in 1.9+ UHC there can be chest loot to please the people.
There are probably more reasons that I cannot think of right now, feel free to comment some down below.
Thanks for reading,
- "Private" / "Jácobo" / "Him"