For my industry (aeronautics) : the problem is not so much to manufacture a part in 3D printing (because this part is already more or less existing) but to explain to EASA (and demonstrate) that it will be reliably constant in its properties.

The demonstration part calls for tests and expert mechanical and material analysis. If -say- we wanted to avoid to store perishable seals and instead develop the 3D printing of seals as a new spare part strategy (which will have to happen someday), we need to be able to prove that the storage of the resin doesn't affect it for XX years, that to have this and that spec in a reliable way the printing needs to happen in this or that conditions.... Tests tests developments.