Apps will not have to be complex to be extremely useful.
In fact, having a large number of single purpose apps is probably MORE useful in encouraging home users to consider 3D than a handful of comprehensive 3D applications that might be difficult to learn. Let's use our imaginations to see just how simple an app might be and still be, potentially, wildly popular.
First, lets examine the output of the app. All it would do is create a simple heart shaped pendent with a partially customized message. We'll call our imaginary app "HeartExpressions"
The customization, in this case, can be as little as having the user enter a name. That's it.
The important thing is to remember that developers don't have to feel that they must deliver comprehensive applications that do all things for all people. Sometimes it is the little things that mean the most. And, I can guarantee you, that if you create an app that I can use to create custom messages in little pendents for special occasions, I will DEFINITELY buy it!
I would like to encourage app developers to ponder the many benefits of simple extrusion in creating 3D Objects that will have broad appeal to consumers. The heart, above, is just one example. For inspiration explore the world of paper crafting. A good place to start is Denise O'Conner's Purple Paper Paradise Blog or Nicole Boucher's Nicki's Cardstock Creations blog both of which are full of creative projects that can give app developers ideas for some very nice single purpose apps that would appeal to the crafting community.