Until people actually visit the depths of the ocean, swim into the sun, warp out into deep space, send their minds into the congested infoverse of the internet, or experience physical contact with God, I'd say pretty much anything that can be written about has been written about, the end result being that the snare of plagiarism is pretty difficult to elude. There are only seven types of story, only twelve character archetypes, seven versions of the Hero... what can be done and avoided being done has been... they're called tropes and there are multiple websites devoted to them. There will always be those who cry plagiarism but just a handful of those would be legitimate claims. The only alternative would be for all record of any story ever to be deleted and have every human have amnesia.