Virtually no chance Arop ever breaks the WR, let alone sub-1:40.
You’re thinking a) 2-3 seconds isn’t a lot, and b) an 800 runner doesn’t hit their physical prime until age 27–neither of these are true.
2 seconds is a chasm at the super elite level in the 800. At 1:42.85, Arop is tied for 30th all time performer, and 83rd all time performance. His progression in recent years has been:
2019 - 1:44.25
2020 - 1:44.14
2021 - 1:43.26
2022 - 1:43.38
2023 - 1:42.85
In 4 years he’s progressed 1.40 seconds and now he’s hit the 1:42s, which is almost a catch-all, with 41 men breaking 1:43 and only 5 breaking 1:42.
And the 800 is basically the young man’s event in track and field. There have been guys who have consistent careers through their early thirties, but a majority run their best times in their early/mid twenties. Marco Arop is 25 years & six months. The ages of the 5 sub-1:42 men when they ran their PRs:
Rudisha - 23 years & 8 months
Kipketer - 24 years & 8 months
Coe - 24 years & 8 months
Amos - 18 years & 5 months
Cruz - 21 years & 5 months
Furthermore, nobody has ever broken 1:42 at older than 25 years & 4 months—nobody has done it at Arop’s age. Sub-1:40? Honestly it’s just a ridiculous proposition.