I can go for Hasbro-style 3.75" of these sci-fi properties.
BSG (70s)
Buck Rogers (70s)
Flash Gordon (80s movie)
Planet of the Apes (60s, 70s)
Clash of the Titans (70s?)
Star Trek
Doctor Who -- Character Options' 3.75" offering was a nice try but short-lived and the humans underwhelming.
While I love your list, I feel like all of those properties actually did have fairly robust toylines. Some vintage like BSG and Clash, some modern like Flash and POTA.
The #1 property for me forever, and it’s so niche I know it will never happen, is Jim Starlin’s Dreadstar comic. I could literally stop collecting all toys happily if I ever got a line of those.
