I have already predicted that Tsitsipas would win the tournament as he had shown a greater talent than Thiem. Also Thiem was under pressure because he was the favorite of the two while Tsitsipas look relaxed and played a great game in the final.
I remember watching Russian up and coming player Karen Khachanov play excellent tennis in the Paris Masters final in 2018. He won that by defeating Djokovic. I had hopes he would break through and get to quarter-finals and semi-finals of all Grand Slams in 2019 but he did virtually next to nothing. He is now 23 years old and is very talented.
Medvedev (another Russian just 23 years old) on the other hand broke through and had an excellent 2019 getting to the US Open final and nearly winning it. I think he will be consistent.
Tsitsipas is 21 years old, had a good year end but I cannot see him winning a grand slam just yet. I cannot see Zverev getting there just yet either. Of the chasing pack Medvedev and Thiem are the more likely to win one. Maybe if Thiem gets to the Roland Garros final again he will win it after all he had two consecutive finals only to be beaten by Nadal on both occasions.
Of the 4 grand slams I think 2020 will still belong to Nadal, Djokovic and Federer in the sense that all three should get to the quarter-finals of all grand slams and at least 2 of the 4 grand slams will be going their way.