A windmill safety shroud unit would be built out of some formation of iron-bars (similar to the chain-link fence addon). When placed in a 5x5 or 9x9 plane centered on a windmill face it would define a region that the windmill's blades operate within. While this would reduce a windmill's output by limiting it to a maximum of 5eU/t; it would also have the benefits of causing the windmill to cease making any other block checks /and/ for it to never break in high winds.
I feel adding this element to the game would make windmills actually look like windmills, instead of like stacks of jet engines stuck on poles. The 5x5 / 9x9 regions would also force wider spacing.