There are multiple addons to slime fun that would make it a lot more fun.
#1 tinker's construct: This would make the use of a single tool way more fun and add a little extra to our weapons and gear. https://www.spigotmc.org/resources/tinker-tools-inspired-by-tinkers-construct-slimefun-integration-available.33731/
#2 lucky blocks: I like this one because you can make thins do weird things. https://github.com/TheBusyBiscuit/luckyblocks-sf
Here are other plugins I'd like:
#1 Mythic mobs, It's a great plugin for making custom mobs or just changing the difficulty of specific mobs. You make custom boss fightes from their easy to learn code. https://www.spigotmc.org/resources/%E2%9A%94-mythicmobs-free-version-%E2%96%BAthe-1-custom-mob-creator%E2%97%84.5702/
#2 Libs Desguises, this goes well with mythic mobs and allowes mobs to disguise as players. https://www.spigotmc.org/resources/libs-disguises.32453/
#3 Artifacts, this lets you use special abilities be tied to weapons. Kind of like the sf earth axe. https://www.mythicmobs.net/index.php?resources/artifacts-mythic-items-and-enchantments-early-access-25-off.37/
Other stuff I wish would be added:
An ability to smelt something to make netherrack (maybe obsidian)
For bees I think. It's a very well made plugin.
I'll add to this list as my brain exploads for now that's all I can think of.