It's fun to see some really old nodes so I don't like the "last x years only" idea.
Instead of the "50 of the top 2000 nodes of all time" how about
a random 50 chosen from the top 50 nodes of each year, 1999-2019+?
Seems simpler, don't need to bother with scaling factors.
Since PM has been going for around 20 years, that's a random 50 from about 1000 nodes.
I further suggest they be displayed in random order and without showing the rep.
Update: Instead of showing the rep, how about showing the year?