Version

More versions -> better
Personally i'm still using 1.12, but will be happy to see it in future verions as well

What Should Be Added or Changed?

I'm using combination of mods like ScalingHealth and Stat Keeper. And the second one only for 1 feature that SH missed:
The only way to restore missed max health is using special Hearts from mod. Would be better if any option in config let us to set the item list what can restore Max HP as well.

Like this:

<
minecraft:fish;3, 1
>

<
[id with meta data], [amount of max hp to restore]
>

Also one little thing that somehow matters too.
If the consumable item is food and player have not full hunger bar then game allows to eat it and only after that Max Hp restoration applies.

Why Should This Be Done?

SH will be ultimate solution with this functionality.
For now it's pretty...strange, SH have so rich config, but still really misses such customization.