Blueprints are an important gameplay feature so they must be available and get tested in alpha and beta. Would be great if we could keep our blueprints so we don't have to design everything from scratch again.
I like the creative mode in Empyrion - Galactic Survival. You can create stuff in creative mode, blueprint it and use these blueprints in single or multiplayer survival games.
Would be cool to have an offline creative mode in DU as well!