I think that would be great, but it's tough to come up with the specific visuals that actually work well. For a mine, an exaggerated visual like the trigger-flash is fine, since that's what the mine is all about.
As much the flux level of a ship is important, it's far from the *only* important piece of information. Effects generally have to be exaggerated to work well, right. So an effect that's a visualization of an ongoing state of the ship really risks overwhelming both the ship sprite and other important bits of information. And unlike armor, which is positional, no such luck with flux.
There's also that the exact flux level is quite important; 80% flux and 95% flux are very different. The nice thing about the flux/hull bars is they are precise, and tend to be relatively small compared to the ship and don't cover it up, so it's an acceptable way to present it.
Something to represent a ship being very close to overload - with nothing at all for lower flux levels - would be more practical, but that couldn't replace the flux bar. Neither could a more detailed effect, really, flux information needs to be precise. And it's still not clear just how that might look.
So, basically: generally see your point, but it's tough, not getting it quite right would be detrimental, and you'd need the flux bar to go with it anyway. Still, I could see adding a "flux is super high" warning visual at some point.