Ah, I see. Actually, what's stopping you from making this work both ways. Let's say you click a slot (which is now highlighted) then mousing over anything in your inventory could also show the changes.
This; it should work both ways, with mouseovers. The 1.001 update is definitely a great step in the right direction, but the drag to compare doesn't feel "right" to me. This is how I envision it:
When you select a part (which highlights it and dims all the invalid slots in the current exo), mousing over any of those slots shows the comparisons. Clicking on a slot would install the part there. Alternately, clicking on the part again would deselect it.
Going the other direction, when you click a slot (which highlights the the slot and filters the parts list appropriately), mousing over any of the parts shows the comparisons. Clicking on a part would install it into the selected slot. Alternately, clicking on the slot again would deselect it.
Going a step further in usability, it'd be nice if when you selected a part or slot, the popup showing its details persisted, and when you mouse over the slot or part, the "normal" popup showing that item's details showed as well. I miss seeing the full details on both parts in the new screen. Obviously there'd have to be a little massaging to make the "persisted" details popup to be positioned correctly to not obscure anything (e.g. computer parts would display the popup above the computer components, propulsion and right side weapons would pop it to the left of those boxes, top row weapons would pop below those boxes).
And also +1 to using the mousewheel to switch exos, since there's no scrolling box o' stats anymore.