If Medvedev even keeps 80 percent of the level he displayed during Montreal-Shanghai, he can reach #2 as soon as Wimbledon. But at the moment, Tsitsipas has the momentum. At GS, Thiem has the advantage if somehow he plays at AO, USO like he did at WTF/IW/Beijing.
i went (...extreme recency bias) with Daniil, who seems to have had a great display today, 24 winners with only 2 UE. highlights have some amazing passing shots.
and he has shown that he can play for weeks at the highest level.
but i am very positive about all 3 players, all three could get there first. i think we are in for some amazing rivalries and epic matches, with the likes of Shapovalov, Sinner and whoever else also rising!
It's been 14 years since anyone outside the Big 4 occupied the top two spots. So, it'll be a noteworthy event when someone else finally breaks into the top 2.
As for who will do it, I think all three are capable, including some others that are not on the list. I picked Tsitstipas for two reasons: first he's the youngest of the bunch, so he has the most room to grow. And second: he's very good on both clay and hard, whereas Medvedev has so far struggled on clay and Thiem is very inconsistent in general, and especially on the faster surfaces.
Medvedev has a chance with loads of points from the end of last year and relatively few to defend. If Djokovic or Rafa fall away he could easily do it. If Djokovic doesn’t defend AO and W he’ll be close I would think, obviously depending on his own form.
Thiem or Tsitsipas will probably need to win a slam or go on a tear coupled with Djokovic or Nadal not doing a lot.
Medvedev as he has the skills and temperament. Tsitsipas I think is a better player but he is mercurial and Thiem just doesn't perform well enough on all surfaces, I can see Thiem staying around for another decade in maybe the top 6 - 10.