Printing should be able to work by plugging the cups-control interface and to launch external applications, you can launch them via xdg-open using the desktop interface. To do this, you declare these interfaces as plugs in the snapcraft.yaml using something like:
apps:
wireframesketcher:
command: opt/WireframeSketcher/WireframeSketcher
desktop: usr/share/applications/wireframesketcherstudio.desktop
plugs:
- cups-control
- desktop
cups-control does not get connected by default, and so after installing and then this has to be manually connected after installing the snap:
snap connect wireframesketcher:cups-control :cups-control
As such I hope wireframesketcher should be able to run as a strict mode snap without the need for classic confinement - my understanding is that unlike Eclipse it is not a general purpose IDE so it should not need the full requirements of a general purpose IDE and so classic confinement should not be required.