I've seen quite a few modded cases and I love them... I've once see na guy with his 5inch bays replaced with a watertank for his water cooling. It was big enough to have a few fishes in it
You can buy ready-made cases with windows and lights, but they are hardly original. Also in my opinion they look to "funky". Advantage is that you don't have to come near your case with a grinder and possibly feck a perfectly good case.
If I were to mod my case I'd go for the new-age stylish look:
alluminium case, edged window half over the top and side, finished with a black rubber.
A red or blue light, depending on motherboard color.
Display in the front with accurate status information.