The thing about sunlight is... most people like privacy in their shower.
I have used bleach but it is sort of a last resort option. I nearly killed myself from the fumes when I stupidly used, first some sort of strong cleanser and then bleach. Very caustic! My eyes burn just remembering that! I have high hopes for the power scrubber... I think it was ehBeth who said she had one and liked it.
We have the right kind of dry wall, there is a big fan and the tile was sealed so all that is OK. The idea of a green plant absorbing moisture is very interesting. What kind of plant do you think would be best when the only natural light comes from a small skylight?