What makes it so huge in your opinion? PayPal and Venmo and the like already make this very easy, internationally there are some challenges, but it’s not technical limitations so much as legal/compliance which doesn’t go away with blockchain.
"Some challenges" is doing a lot of work there. That's like saying that a hurricane's "a bit of water". If you're in Montana and don't have any family in Florida, you can blindly ignore the hurricane as it won't affect you. But realize that's a position of great privilege. For everyone else that can't get Paypal or Venmo or even US bank account in many case, or anyone who's Internet access is solely WhatsApp and not Venmo (due to Facebook providing free access to their properties and only their properties in certain countries), this is a total game changer.
Whatsapp has 2 billion users, PayPal and Venmo probably only small fraction of that.
On Whatsapp you already have your friends in the list, on PayPal I personally have nobody. It's an additional hurdle, I've never actually sent money to friend/family through PayPal.
However, thinking of this only in terms of this this will affect you is short-sighted, and apes other hot takes that went down in Internet history (HN on DropBox, /. on the iPod). The broader context for this (as discussed in other threads here) is what makes it interesting. Similarly, from a product POV, Twitter doesn't look like much - it's the users that are on there that makes it interesting.
With crypto under the hood, it becomes quite easy for competitors to build a remittance product.
They make it easy because they abstract away the underlying mechanics. Novi for WhatsApp does the same, but for a much, much larger audience, and does so instantly. While it isn't shackled by the baggage of the financial industry born in an era far removed from the current one, the pace of improvements and deployments can be much faster in face of changing regulations, jurisdictions, and technology itself.
International, fee-less, instant payments? With the amount of ecommerce that happens over WhatsApp and Instagram these days, Meta stands a very good chance with USDP to cut out the middle-men (all of the legacy financial infrastructure) and take the product straight to the consumers. Sure, Meta could partner with PayPal, but Novi is a better, if ambitious, bet.