what they are using is some custom actions (you can make those in the actions menu) to hide tracks without items.
It won't move tracks to top position. only hide the others.
It would be easier if Reaper would have a way to split the arrange window in two and move some tracks to the top split window. but meanwhile, you can just hide and show tracks. Cubase has split window since ages... but it didn't have track visibility until recently... so now it's Reaper's turn to do split window
I used to have big templates with many tracks... but I now prefer to use track templates and load them as needed. so I don't have hundreds of empty tracks and just load folders of tracks when needed.