This isn't brand new. Here's a bunch more links that you can read from write-ups published by some of the Internet travel bloggers:
https://viewfromthewing.com/bask-bank-savings-account-earn-miles-for-saving-money/
https://frequentmiler.boardingarea.com/bask-bank-savings-earn-american-airlines-aadvantage-miles/
https://thepointsguy.com/news/introducing-bask-bank-a-new-way-to-earn-miles/
Notice that you're going to get a 1099. How much that hurts (how much that diminishes the value of the miles awarded) depends on your income tax bracket.
You're earning miles rather than interest. But in a very low interest rate environment, you're not giving up a lot of dollars in bank interest. Most banks are paying peanuts these days, and then those peanuts are taxable.
You will then need to redeem your AA miles for flights on American or its partners. How good a deal that will turn out to be will depend on the availability of award seats and the "cost" of those award seats in miles. There's nothing to stop AA from making award tickets more difficult or most costly to obtain (that is, devaluing their award program).
Although I don't have a Bask Bank account now, I did have a miles earning BankDirect account in the past. It allowed me to build a good-sized stash of AA miles at a time when interest rates were very low and those miles have served me well for award redemptions. A poster above me says that AA miles are worth 1-3%. I'll agree, but it has gotten harder in recent years to get much more than about 1.5% (1.5 cents per mile) when redeeming for an award ticket.
I'll admit that I'm thinking about opening an account as well. In the current interest rate environment, it's getting harder and harder to find places to stash your money where you can earn any reasonable return.
What's a reasonable alternative? Do you have an Ally Bank account?