Unfortunately this isn't feasible to do because of how the vault stores items. To do this would require a lot of extra code to handle merging stacks and splitting them apart, and would cause vaults to be even larger (as in, take up more data) and less efficient. I don't want to say this will never happen, but for now it's not feasible. Sorry.

As per an official response had been made. Therefore since it not feasible as of now I will be locking this.