Unfortunately, I’m not able to talk about the exact rules but we already use a variety of methods to greatly reduce the number of times you are asked to authorise payments.
3D Secure 2.0 launches this year and with it comes a number of improvements particularly around payments in apps (the original 3D Secure specification was written well before phones had web browsers!). This should fix a lot of the issues like the one described in this thread.
You will also see a lot more merchants and other banks pushing transactions through 3D Secure as part of their legal obligations under Payment Service Directive 2’s Strong Customer Authentication requirements. I don’t know how Amazon plans to get around this. 