Here are those metal button light option mockups I promised. I used plastic buttons because I don't have metal yet:

The design goals are:
Add colored lighting to metal buttons.
Minimum disruption to the beautiful metal surface.
Allow colors to be changed.
Keep it simple to keep costs down.

The red on the left are 3mm end glow fiber rods. The green on the right are 1.5mm end glow fiber rods. They are long enough to be close to the LEDs, but not touching, even when the button is pressed. I had no idea how to polish the ends, so they could be even brigher if done right.

The rods are simply pushed into holes of (almost) the same size. They are not glued so they can be popped out and replaced with other colors.

Does this modification satisfy your metal + lighting needs? I could buy a drill press and make this modification as requested. Or, with enough interest, have the machine shop punch a certain amount. I plan to include a full rainbow kit of lighting rods; one set of each color, so you'll have them when you need them.

Then the size question: 3mm or 1.5mm or either? Allowing for either would work with enough interest. Otherwise, it's best to choose one size for all lighting rods.

I hope this give you the best of both worlds. Let me know what you think.