Nubank, the Brazilian bank unicorn, described their approach as “if this works, it’s because we reached massive scale quickly” (paraphrased) and started with an

Nubank, the Brazilian bank unicorn, described their approach as “if this works, it’s because we reached massive scale quickly” (paraphrased) and started with an architecture that would support that from the beginning. They were very happy with their choices and have blogged about them in detail. This is a case where “things will be much easier when we scale to a massive number of clients” turned out to be true.