ACADR14 comes with a function called SOLPROF that does this.
1-go to model space. if you do not have any viewport setup, invoke the mview command from paperspace and create 1 viewport of any size.
2-in modelspace, select the view of the solid you want to "flatten" (top, front, right,...).
3-type the command SOLPROF, select the solid, accept all defaults.
4-now your solid is represented as lines only. there are two layers created, one showing visible lines and the other showing what would be hidden lines.
the only works for solids. xrefs and blocks will need to be bound and/or exploded for this to work