My hot take is that underwater photography requires unusual equipment and you'd have less competition than the others. For webapps I'd want to see some clarification: do you want to fly your flag as a mercenary web developer? or do you want to develop web apps that make money for you directly?
I would also look at teaming up with people.
In the last year I've gotten interested in art projects such as interactive cards I print, persistence of vision displays, video game characters projected in a mirror, etc.
I just ran into an old friend who showed me an art exhibit made by about 20 of her friends where you start out in a mad scientists lab (where there are some one-of-a-kind coin op video games) then you go into a "time blender" and get sent out various doors where you might go to a crystal cave, or the bottom of the sea, or a map room where there is a sand table that is scanned by a Kinect that has contour lines projected onto it.
Then and there I realized I could accomplish a lot more as part of a group than I could myself.