Waiting for the day that printer will be able to print copies of itself.
3D printers are just another tool in the manufacturing toolbox. The sets of materials and structures printers are made from barely overlap with the sets of materials and structures that the same printers make.
If 3D printers could make themselves, I think they would look a lot more like biological organisms and a lot less like laser copiers.
That said, the Desktop Metal parts I've seen are beautiful.
Much like people think that the only thing standing between them and designing cool new useful software is all that pesky syntax, and that if they had some magic application to turn pictures into software, the rest would be easy.
http://www.wired.co.uk/article/artwork-selling-itself-on-eba...
Although, I think if they end up able to print robust, ready-to-use metal components with reasonable strength (say strong enough for a bicycle frame), that would be a pretty good leap forward. The base tech of what you can do on a desktop doesn't seem like it would quite get there today though.