For me (from a coder perspective, as the height of my artistic talent was epitomized when I learned to draw stick figures ) useful features would be:

• Low poly spline based modelling. Good tools like extrude and lathe to use the splines.
• Good coordinate system for determining hard points on a model.
• Ability to export .obj files
• Multiple textures, including base texture and optional bump maps, specular maps, and light maps (.mtl files).
• Adjustable quad pane window setup (top, front, side, and perspective views), so I can grow the top view very large while shrinking the other view to fit, with a menu to revert to defaults.
• Very quick and easy controls for rotating, zooming, and panning around viewports, with a quick way to get back to a normal view. (something which is usually poorly implemented, I find)
• Good set of preview rendering capabilities, maybe the ability to do OpenGL renders using custom configured lighting and material setups? Spot renders (as in Infini-D, very useful).
• Translate model based on COG calculation (volumes enclosed by model?) or by simply picking a coordinate to be the new center.
• LOTS of undos! Maybe even some sort of internal versioning system?
  

Bones and motion properties would not be useful for me at all (doing space-ship models), so maybe a way to turn off, or hide all those features so they don't confuse me

I'd love a modeler like Animation Master. The process for model development is very intuitive in my eyes.
(However, a 3-D app that doesn't quit/crash/and bug out unexpectedly)

-The model will be "spline and patch based" retaining limitless resolution and editing capabilties. User selectable subdivision of patches for low polygon count when exporting for game.
-Exportable model in all industry standard formats
-app capable of importing pict/tiff image as a window background or separate resizeable object (this allows modelers to trace the different views of a drawing/illustration and more precisely model the character.)
-hierarchical grouping of 3-d objects and forward kinematics system (i know this is an old school approach but that's how 3D animation was done 6 years ago.) if possible, but not needed, inverse kinematic system.

I think for a 3-d based app to be useful for the masses it'll be best to allow modeling, texturing , and animation within the same app.

this way the app can be used for any kind of medium (game/mechanical design/3d film, etc)