I think it would be great if I could get a list of all my unique captures or hacks. What do you think?
You still can. You can request your personal data and all info from Niantic and they will provide it to you. You will have to wait something about a month for it though.
I agree it would be great to have info on scanner that portal was already captured/visited. Fortunately there are plans for something like this after redacted retire.
You know, I was thinking about asking this same question just today! Niantic already provides this info on another game (that I will not mention here) and I find it quite useful. Being able to know which portals you have visited / hacked is quite necessary. Especially if you're traveling the second time in a big city and you're looking to do some uniques!