There are many possibilities to find similar 3d objects, like the "Shape DNA" algorithm. You could group similar models and save a lot of clutter from duplicates when searching for something in your database. I can provide more details if you are interested.

nurbs

I find that I am often distracted finding out what view I am in (right, front, etc.). If the viewport had a different colour border or the drop down choice was a different colour, or even if the background was a different colour, it would be easier to be aware of which view you were in.

provide extrusion of a vertex to form a new edge

It would be useful to have a short description of what each tool does when you hover over them with the pointer or stylus (for tablet pc users)

Please add Alembic or FBX's vertex cache format support.

integration of the Houdini engine would be massive.
https://www.sidefx.com/index.php?option=com_content&task=blogcategory&id=227&Itemid=381

As stated, being able to export to an AVI. if you have please tell me how. also an offline editor would be cool.

How about subdivide a face?

terrain and heightmap tools

Because it is sometimes difficult to quickly understand where you are viewing the scene from, I suggest you add more clues like colours of the axes on the centre lines of the grid and/or a small axes indicator in the corner of the view.

More free scenes :P

Clone popups dialog box every time, very depresive if ya need to duplicate lot of stuff :)

p.s short keys !!

UV MAPPING + TEXTURE GENERATION + PROJECTED PAINTING

Annotations
I'd love to be able to attach annotations to models (like on sketchfab)

Import Skp file

gas textures

Soft Selection

LuxRender, Blender Cycles, or Corona Renderer support.