Could there be downsides to this function?
The feature in itself is. In order to be eligible for this, you have to store your coins in Binance, so what other downside are you looking for that could be worst than that. Congratulations to cz and binance for always coming up with ways to encourage people to store their funds in the exchange, the other time cz was saying 99% of people would lose coins in their self custody and now this.
If you are looking for an inheritance plan, i recommend you use one that doesn't put the custody of your coins in the hands of a third party, so you don't lose your coins while you are still alive, lol.
CZ is a very smart guy and always comes up with features that ensures longevity and dominance of Binance in this crypto space. This feature would convince a lot of ignorant masses that Binance is safe for a long-term and increase their trust for the CEX, while in reality, they are placing their funds at greater risk by leaving it there.
Personally, anything that keeps my funds in the hand of a third party for long is a big
NO for me. It is always non-custodial for long-term storage or nothing.