Wow another one?! This one is very different from the mining one.
ABOUT: Forging weapons into another form
There will be a new thing called Weapon level.
All the damage the air damage etc will be doubled if forged
there will be 5 levels of each weapon
to upgrade to level 2 you need 2 weapon of the same item
go to the blacksmith npc and he will forge it
FORGE TIME: 1 Hour ( 500 gems to speed up )
editing more…
The weapon will get stronger each level.
Hmmm this could work very well but it has to be done right not to make it too op
Too overpowered and complicated, is all weapons is affected by this forge upgrade or no?
There should be a new sword (familar with crappy pickaxe) but with no durability and can be upgraded to epic sword?
I would say first GOOD IDEA.
But if you would do that i think you should do the same for armor things, because as already said that would be too OP.
To overpowered.
If you say all the damage & the elementals damage.
The normal damage on a weapon is 100+
If u double that u would get 200 damage
Maybe its better if they do this update but they add like 5 damage in plus , not double.
Edit 
Each upgrade 2+ all the elements