Yeah, this process is tough (which is why there hasn’t been much movement).
There’s one process for individual city collection if the city exists correctly in Open Street Map. That’s covered in the README in my public collection of city data.
There’s another process for individual city collection if the city doesn’t exist correctly in Open Street Map. That’s sort of covered in my reply within this issue. It’s super painful, inaccurate, and I don’t suggest doing it. 
There’s yet another process for bulk data collection (which I greatly prefer, where possible). I don’t have this documented anywhere - it’s a collection of scripts I’ve cobbled together. It collects data on the Region level (which is defined differently for every country - in the US this is each State, and in Canada I think I’ve been using the Provinces), so I can grab many cities at once.
I should take another look at the processes/scripts to see if I can extract any of it into usable tools for people to help out with… 