DannyT is right about repetitive tasks or "macro"
There should be a way to script MoI, let the user create new buttons (with a script behind)

You could even build an entire dimensioning system by scripting existing MoI tools :)
It's important for two reason, first one is that you can't always expand the feature set while maintaining the UI complexity at a very low level, second one is that some people have very specific needs and that's directly related to the first reason.

But it's not just about having a scripting language and creating button, the whole UI should be re-thinked but not in his form but in the functions, for example letting the user re-organize the buttons like he want, create panels, collapse things etc... That would also help people with multiple screen-setups. Without that you can't let people create new buttons, because it would be a mess.

For my point of view, the current MoI toolset is almost perfect, I use 90% of the tools, and only 5% of the time I need to switch to another software (for example, paper plotting, dimensioning, hatching etc...)

So instead of adding new features, I think it would be more logical to use the existing set of features and let anyone create combinations of them. Kinda like lego blocks, MoI already got the most beautifull and robust lego blocks ive seen, but you can't really put them together :D

Also one big thing missing is xref, or instances.
For example you got 32 screws in a model, all in place, and you got 1 screw at the origin wich is the original model and everything you change to that screw is mirrored to the other screws. That's not really parametrics but that could help.

With instancing + scripting you could make fake parametrics.
For example you draw 1 circle on the face of a cube, instance it three time on the other faces of the cube.
Then you do a hole script (extrude in the direction of the closest surface, inside the cube, by 3cm, then boolean)
So here you got a cube with three holes in it... And then you need to change the radius of the three holes...
Instead of undo-ing or filling the holes with booleans. You just pick the circle you used for the hole script.
You change his radius (all the 3 other circles change radius) at this point the three holes didn't changed.
You run the hole script again on this circle, MoI remember the last settings used by this script.
Since MoI remember the last settings, he ask you if you want to fill the holes, you say yes.
By using the last settings he do the inverse thing, he create extruded circles, and do a boolean union.

At this point your cube has no more holes, the script is still running.
You input new settings (for example 3.5cm deep, then boolean) and MoI do the rest

It's like parametrics, without parametrics... Isn't that cool ? :D