I think the problem here is that they choose a technology that is difficult - but not impossible - to scale, and they didn't have either the in-house know-how to solve their problems neither the money to hire someone with the knowledge to do it.
I think RoR could have been a good decision a few years ago, when the web framework landscape what atrocious, but nowadays there're a lot of good options based on other programming languages that have already proved could be scaled without finding untraceable bugs. Heck, just a few days ago an acquaintance showed me a webapp running over a perl - Amazon, IMDB, Slashdot... use perl heavily - async framework 20% faster than node.js.
Ok, I'll tell 37signals that it's time to shut down Basecamp. You get on the phone with Shopify and break the bad news.