Idk, possibly. Maybe if you piece together lots of chunks of data hidden in the witness section of a transaction, you might be able to interpret an illegal image etc, but because it would have had to have been hacked in in multiple chunks, it is neither obvious nor supported and so a fork is not nec...

Edit: a fork to remove the illegal data is not necessary. A softfork to prevent it being put in op_return may be warranted.