Really excited to see this feature finally being introduced. 
It’s a great start but I’m honestly really looking forward to the fast-follows mentioned…
This sounds the most exciting one of them all!
Hoping that will address the below request; the main difference being the ability to referencing a specific project or portfolio (just like @Esteban_Giannini just mentioned above) and presenting their contents (tasks/projects) in a dropdown list, instead of a ‘pool’ of searchable objects, similar to how dependencies or tags work.
But unlike dependencies, my initial tests of the Reference field, conclude that they do not back-reference one task to another. With dependencies, when you make task A ‘Blocking’ task B, then when you open Task B, you will see it is ‘Blocked by’ task A, automatically - that is what I refer to as back-linking. Unfortunately, the new Reference field doesn’t do that - it is currently one-way linking which, in my view, is an initial shortcoming of this MVP. 