According to the article, the upgrade took 1 year for 3.2 > 4.2, and then just 5 months for 4.2 > 5.2. The project began with one FTE, and some volunteers, and expanded to 4 FTEs. But the author says almost none of them had ever done a Rails upgrade before.

I'm curious to what you think would be a better framework for Github to have used, that would've allowed for easier, speedier point upgrades? Rails likely was a big advantage (as it usually is) in the initial stages. Are you seriously expecting it to be just as smooth when the site experiences exponential user and feature growth? That moving from Rails 3 to 5 was doable, with what sounds like a small team and no massive service disruption, seems like a very strong argument that Rails can still be effective in a company's middle-age years.