Honestly, I could care less about the HK-55 Bonus Chapter. Sure, it's a shame to miss that but as someone has said, it's completely missable.
My issue is that fact that you needed to sub to keep HK-55 after a certain point. He was already in the game, and now all the people who chose not to sub are screwed out of a companion. Again, the chapter isn't my issue and all things considered it was a good business move.
However, KotFE itself has been released for over two years now (October 27th, 2015) and on January 11th, 2018, it will have been exactly two years since the HK-55 Sub Event (if you can call it that) has passed. Sub rewards have been given out before, although very sparingly (Kakkran Daggerstar and only because KOTOR came to Xbox One) but I feel that I can at least try to bring a solid argument to the table for allowing everyone to have the alert Arma Rasa at least. Niko Okarr and Shae Vizla aren't tied to the story as a whole; HK-55 was already in the story before he did his thing.