The article is behind a paywall but...
Wealthsimple isn't even a bank, let alone the next big bank. They are not a deposit taking institution. Their 'savings account' is just an agreement with a number of actual banks to accept deposits from Wealthsimple on behalf of their clients. Wealthsimple is merely acting as an intermediary.
Being a true deposit taking institution comes with a lot more regulation and institutional sophistication. Never mind the fact that deposit taking is only one side of what truly defines banking: aggregating demand deposits to enable lending. I'm sure Wealthsimple is looking to get into that game, but since they aren't deposit taking I'm sure it will just be a pretty wrapper around another actual bank just like their 'savings accounts'.
Is Horizons ETFs the next big bank because of their CASH.TO ETF? Horizons is doing a very similar thing through a different vehicle.
Having said, Wealthsimple has clearly created a competitive product suite. But their ability to offer these products fundamentally relies on other organizations (e.g., Mastercard, Big 5 banks) to do the heavy lifting. Wealthsimple's competitive advantage is in product design and advertising.