If you'd ask me for a new MoI functionality top 5, in order of importance to me personally, I'd say:

1: More robust fillets, capable of handling any complex set of edges.

2: Optimized high-res polygon mesh to NURBS conversion, resulting in as few patches as possible.

3: Fully quadrangular meshing as an export option, similar to ZBrush ZRemesher / 3D-Coat Autopo, with a smooth edge loop structure that follows the flow of a solid, ready for subdivision.

4: An improved History system that remains intact longer, or maybe even better: a modular modifier system like in 3ds Max. For example: a Fillet modifier that non-destructively auto-adds fillets to any sharp edges in a model, and can be adjusted at any time.

5: More flexible solid editing options, such as the ability to manipulate edges and surfaces of solids more or less like polygonal control and/or using adjustable FFD/Lattice cages for object deformation.