I doubt that 2020 is reaching 2007-2009/2011-2013 level.
It's not really Tim fully realized. The great promise was his serving and Alcupoco 2016. With teams super kickher he had extremely high first serve percentage, aces and serve points won. Unfortunately he had to dump that serve by the end of 2016 for medical reasons. The super kicker was never even close to what it had been. This is something he can never get back.
I am making a call that next year, at this stage, looks exciting. On paper and results-wise the last 3 or 4 months point to itMaybe I'm in the minority, but I never get tired of seeing Djokovic Nadal and Federer being #1, #2 and #3 and winning the biggest tournaments. It can continue for 2, 3 years and maybe more, I won't complain. I have the feeling it's changing but the fact remains, they are still #1 #2 and #3 at the end of 2019. What will be the top-3 at this same time next year? Will Medvedev, Zverev, Tsitsipas and Thiem take over, or will they remain #4, #5 #6 and #7? Can Wawrinka and/or Murray fight for the top-5 again? Medvedev and Tsitsipas weren't expected to play the ATP finals at this time last year... maybe there will be new players like them in 2020... Some that are between #20 and #50 now, and will be playing the ATP finals next year? I think of Shapopalov, Auger-A, DeMinaur in particular, but it could also be Khachanov, Rublev, Kyrgios, Fritz, Opelka, Garin, Hurkacz, Humbert, Kecmanovic, Tiafoe or others... Perhaps one or 2 of these players will imitate Med and Tsitsi and be in the top-8 next year.
The most important question is who will win the Slams... As good as these young players have been, Djokovic and Nadal won the 4 most important tournaments of the year. Thiem had catastophic results outside of the French Open. Tsitsipas had quite poor results after the Australian Open. Med reached the final in the USO but couldn't do better than a 4th round in the other tournaments. Zverev made 1 QF and 2 4th round... clearly not enough. The day Medvedev, Zverev, Thiem, Tsitsipas or another player wins a Slam, reaches 2 slam finals or 3 slam SF the same year, this is when the trio will have to worry. As long as they win the Slams, they'll be safe.
One difference is that the Big 3 (Djokovic in particular) had a lot on the line at this WTF. I think there are 6 genuine chances at the AO next year: big 3 plus Medvedev, Thiem and Tsitsipas. That's a healthy position for the sport.Or it could be another false dawn, with the big 3 dominating the slams again. The WTF is becoming a consolation prize for underachieving players (Dmitrov and Zverev have won the last 2 editions, and this tradition will continue this year). Medvedev is probably just tired and burnt out by a great season, but it's worrying for him if even players of his own generation are gaining confidence in wins against him. Never expect too much from Zverev in best of 5. I'll believe Thiem can beat Rafa at Roland Garros when I actually see it.
I think Thiem and the NextGen will have more success in non-slam tournaments, but it's been that way for a few seasons now.