I don't think it'd be very secure due to the connection method (Bluetooth). When you have your smartwatch connected to your phone, you have to keep the bluetooth permanently on. Watches can be exploited and other devices could pair with it if the smartwatch has the option to deny access to unknown devices turned off. I'm no security expert but I am sure that even with all security options turned on, they still pose a risk.

A 2015 test by Hewlett-Packard (HP) resulted in 100% of the smartwatches successfully exploited.
If that's too old, a 2018 Kaspersky security research on smartwatches ended in negative results too.

Smartwatches are cool and all, but they haven't been around long enough yet imo to be considered secure enough to have Bitcoin wallets on them. An idea I would go for though would be an app that would display QR codes for addresses you'd input from your phone on a list. The only risk you'd be exposed to is having your public addresses exposed to a hacker.

If a wallet would be released for these devices, they would become the next target for hackers. And as today I don't think many hackers are focusing on smartwatch vulnerabilities because there isn't much to be extracted from them, such news would make them turn their focus 180 degrees straight to the smartwatches.