I use the "estimated repayments" screen we have now, because the word "final" is written next to the loans that are expected to finish paying that month. On or shortly after the 15th of the month, I go down the list, and click to open up the loan page of each loan marked "final." If the borrower paid on time, and the net billing process or a payment from the MFI results in me getting the credit on time, then I get to see the fact of 100% repayment when I open up that loan page. I recall the reasons why I chose that loan, I feel proud of the borrower (especially if they were delinquent for a while but managed to catch up), and I think warm thoughts and pray for the borrower and her/her family. In a couple of cases, I posted the loan photo from a completed loan here on KivaFriends, with some words explaining why I am particularly fond of that loan and celebrating the loan's completion.
Unfortunately, those "estimated repayments" entries disappear on the 1st of the next month. So any late payments would mean I don't get to do this when the borrower finally does make their "final" payment. I would use a "recently ended loans" section in the same way I now use the "estimated repayments," but for loans where the final payment came late. And I might someday learn to use spreadsheets and use it somehow for that, but right now I don't have that skill.

If I were to receive a special "recently ended loans" email update, I might leave a "comment" to the update, in response. I do that often with the updates that announce full funding at the start of a loan, saying that I hope that the borrower will have good health and prosperity. But so much time elapses between when the borrower makes a payment, and when the credit comes to me, that really the loan is old history to the borrower, by the time I hear that final payment has been made. That lapse of time might deter me from leaving a comment.
I love David's idea of a photo related to final payment of a loan. But it sounds a little resource-intensive, to upload additional photos. Maybe it would be better to have a "recently ended loans" update email, or "recently ended loans" section in Portfolio, that would work automatically, without requiring any Field Partner employee time.
I agree with previous comments about "currency loss" not affecting how I would feel about a borrower, who had repaid what s/he agreed to repay. Defaults are different -- but if you leave them out of the new section, then you may want to call it "successfully ended loans" instead of "recently" -- otherwise, it's not accurate.