The key with 3d printing for manufacturing aircraft components (particularly titanium) is the low level of material wastage involved compared to conventional production. There was an article on the 787 recently in a major news outlet and Boeing's stated prime aim was to reduce the percentage of loss, which is currently mind-bending, given the huge cost of the raw material!
Though not having to wait for 'just in time' spares would be nice. Although the RAF would by 1 printer between 3 units, and it would be the old kind that uses a cable no one makes any more...