The Ultimate Arrow "Who's in the Grave?" Theory Roundup

Arrow season 4 spoilers.

Going on the Arrow sub-reddit there seems to be several "who's in the grave?" everyday. I suggest having a definitive roundup of who could be the person theorised about so much. Whose death would have the biggest impact on the show? Are Felicity and Thea in the clear now that they've survived near death experiences? The writers/show-runners say Felicity is not in the grave, but could her body be elsewhere and the Felicity in the car with Oliver be a hallucination much like Shado was in the flashbacks.
What about Oliver's son? He seems like the next character the show is teasing to die after Malcom told Darkh about him. Would a character the audience has seen maybe just two times leave a big enough impact on the viewers? Would they even go so far as killing off a child? Even with its somewhat darker tone, Arrow still doesn't seem like the sort of show that would do this.

This should aim to be the definitive piece for the "who's in the grave?" theories. Which characters make sense? Which characters don't?

Prime candidates: Diggle, Laurel, Felicity, Thea, William Hawke and possibly Quentin Lance.
Finally, is this who grave talk taking away from the rest of the show? This seems like a tunt to get the fandom in on speculating who is going to be killed off when this could have been handled as a surprise death.