Uncharted 4 seems like the obvious answer but I doubt it will outdo Uncharted 2, which I would consider to be just on the outside fringe of the Top 20 games of all time. Btw I strongly disagree that GTAV is a Top 20 game, given that I was unable to even bring myself to finish it unlike every single one of it's predecessors. As the years go by, people will look less and less fondly on GTAV IMO. If you listened to people when GTAIV came out, they were telling you it was one of the greatest games ever made by GTAIV is a distant memory now for most, loved by very few. Based on the OP's criteria, I would say that Last of Us is the last Top 20 game to come out, which incidentally came out in the same year as GTAV.
It's a good question but I'm struggling to think of one. We may have to wait as long as whenever Red Dead Redemption 2 is announced. Maybe The Last Guardian? Maybe Persona 5? I doubt either of these despite writing them. There are so many great games coming out in the future but none of them looked like they will be phenomenal (and I mean that word in it's literal sense). Given that gaming is 30 years old and we have to predict a game to enter a small group of Top 20 in the near future, its hard because the near future doesn't have any games in it that seem like Top 20.
Fortune favours the bold.
