I agree. That would be an excellent feature, one that I've seen on a couple of iOS apps.
The only issue is that this would be something that Google would have to add to Android because only then would app developers know that the feature is available. Then they can program their apps to utilize the gesture.
I have no doubt GrapheneOS devs could add it, but none of the apps we use would "understand" this new gesture.
Hopefully that makes sense.