I think the reasonable worst-case scenario here is that professors include a mention in their syllabus that certain works contain issues like sexual trauma, abuse, eating disorders, or things of that nature. I'm sure there are others. And maybe a brief mention during the course of the semester when it's appropriate. That's a difference of a paragraph and about ten seconds of talking. Not a huge deal.
I think the incredibly unlikely (but I suppose plausible) worst-case scenario is that all works of literature have a page labelled TRIGGER WARNING in between all the various pages of copyright that nobody reads. There's probably an environmental impact there, but again--I don't think it's super significant.
More seriously, yes, I'm sure people will want to take a mile once you've given an inch, but I've seen enough PTSD flashbacks to be willing to give the inch regardless, even if it means you have to fight the people who want a trigger warning for a character stubbing their toe.
Somehow students survived for decades/centuries reading works like
Metamorphoses, To Kill A Mockingbird, Crime & Punishment, Huckleberry Finn, Things Fall Apart, The Bible. Yes, the Bible. Will the Bible also get a Trigger Warning?