The OG audio and more doesn’t need to be preserved anymore, MAYBE, due to the release of the ALIEN: 40th Anniversary 4K UHD. It’s amazingly on a BD100 (Triple Layered Disc!), is incredibly stellar with great amounts of detail, film grain is preserved, and multiple audio tracks. http://dvdcompare.net/comparisons/film.php?fid=50198 https://caps-a-holic.com/c.php?go=1&a=0&d1=5205&d2=13061&s1=48549&s2=130233&i=2&l=1
Anyway, anything which is not included on the ALIEN: Anthology 6-Disc Blu-ray set, PROMETHEUS, and ALIEN: COVENANT physical releases or is still in print. The previous bonus feature fan discs which were at best on DVD5s could be re-encoded to be housed on BD25s via AVC codec. Content still available solely as Streaming could possibly be featured on a disc if possible. OOP counts too for preservation.
(ALIEN, ALIENS, ALIEN³, ALIEN: Resurrection, PROMETHEUS, ALIEN: Covenant. AVP Duology doesn’t count but the video game Trilogy does but that’s an entirely different matter. ALIENS: Colonial Marines & ALIEN: Isolation. Former is a buggy mess though.)
No idea if these shorts count since they’re only online for streaming, not disc or digital. https://avp.fandom.com/wiki/Alien_40th_anniversary_short_films
Just throwing out random suggestions.