Ever since content in Destiny 2 became sunset, we've lost the ability to obtain countless different ships, sparrows, ghost shells, shaders, and emblems. Despite this, people who did obtain them when they were available are still able to regain them in the Collections tab. With that in mind, we have systems to obtain previous exotics and even items from previous seasons, and so, I believe the next step would be to introduce some kind of mechanic or system to allow you to obtain these currently unobtainable ships, sparrows, shells, shaders, and emblems.