I don’t see why that would not work.

There are foils available that would be much less of an installation problem.

did you post another dilemma regarding this?

I answered it earlier and posted pictures.

yes, just cut the mirror to fit along the back. you can get 12x12 mirror tiles (or peel and stick subway tiles) pick up a glass cutter/scorer so you can easily cut them. affix w/mirror adhesive.

Get a hand mirror and put it behind the items that are in your cabinets to see the effect. Mirrors should reflect something beautiful or interesting. If they will be covered with solid items, book backs and other utility items, they won't reflect light or pretties. Maybe you should add the same kind of lighting above the cabinets as you have below. That will eliminate the dark space above them and should brighten the ceiling too so the wall and ceiling will recede a bit.

Install lighting above all the cabinets

Install lighting inside the glass cabinets

Install light fixtures on the walls above the two sink windows

If all that doesn’t work, then add the mirrors!