There are bakeries that can decorate cake using inkjet or screen-printing machines (with edible dyes, of course) but the logo on this cake was hand-painted.

The icing is done by hand. You can buy stencils for the lettering.

I guess an SVG of the logo can be used as a template to cut out paste.

But you raise a good idea: 3d printing of sugar "stuff" to print messages for cakes on demand, in any font.

Printed edible sheets to put on cakes already exist.

Maybe you can use 3D printers to make "impossible" cakes like crystal structures (ie. Dr. Manhattan on Mars)

Well, at least there's CandyFab [1] which literally 3D-prints sugar. In its current incarnation even edibly so.

[1] http://www.candyfab.org/