First, I think this has great potential. Really looking forward to what the actual release implementation looks like.

But I am curious why the finalizer (as an interface) has to be attached via System.attachFinalizer with an implementation of a separate class. I guess I was expecting that, as an interface, I could simply implement the methods from the interface directly onto my queueable class: "public SomeQueuableClass implements Database.AllowsCallouts, Queueable, Finalizer"

Any insight you could share would be great!

Thank you and keep up the great work releasing Apex improvements!