Do it

This is what went through my mind when I read the suggestion.
I can absolutely see it being used in a trollish manner.
Maybe punishments can be more severe for people who hide inappropriate content in a spoiler tag though?
That would eliminate any of my negative thoughts. I'll vote yes, despite thoughts of people misusing it, it's a great tool. I hate opening threads about TV shows that I haven't seen every episode of.

I'm sure there could be ways around this, i.e. having the spoilers always open to mods or simply disabling pictures etc.

My yes.

They'd be directed to the reported post, and the number of spoilers per post would surely be limited like he number of images or youtube videos are, so finding the issue wouldn't require time or effort. Or if not mods could have spoiler boxes automatically open like Sia says.

Seems like it would be useful.
Most of the other forums that I've been on have similar spoiler options.

Voting yes here.