Procedures were an amazing addition to MCreator. Now nearly everything is possible. However, variables are still very limited.
At the moment, making something with variables makes a lots of troubles: if you use a local variable, it resets every tick, if you use a global variable, it resets when you close minecraft and it's shared between all the worlds.
So, here are my suggestions:
1. Renaming local variables to local tick variables
2. Renaming global variables to something like "minecraft session variable" (I'm bad at thinking of names)
3. Adding world-dependent variables that aren't shared between worlds and aren't reset when closing Minecraft
4. Adding player-dependent variables: they can be useful for new overlay bars, advancements like "collect all these items" and something more advanced like custom extra-inventory slots (I don't want to explain them here but with player-dependent variables they are possible to make)
5. Adding item/block/mob dependent variables stored in NBT data of the item/block/mob
I hope you will add some of these
Sorry for bad English