"DEATH IN HEAVEN"
Missy's "Master Plan" was to revive all of the world's dead as Cybermen, and then hand control over them to the Doctor. It must have been her mad intent to show that he was just as bad as she was.
Most of those dead would have been zombie Cybermen, their minds and souls long since fled. The ones who would still have their souls attached were those she personally culled at the moment of their deaths. Missy focused on those who had some connection to the Doctor and used her TARDIS to collect them throughout human history.
We only saw her collect a handful of characters, and only those who died this season: CSO Matthew, Gretchen Allison Carlisle, the Half-Face "Man", and Danny Pink. (And we definitely know she garnered the Brigadier when he died in Peru.)
Missy must have been gathering up others who died in episodes from the classic series and from earlier in the reboot years - people like Lynda with a Y, Rita, Harriet Jones, the real Margaret Blaine, Sarah Kingdom, Dr. Edward Waterfield, Tobias Vaughn, and everybody from the lighthouse at Fang Rock.
Missy probably collected the mind/souls of those who (hopefully) died long after their encounters with the Doctor: like Cameca, Victoria Waterfield, Richard Mace, HG Wells, and even his wife Queen Elizabeth I.
We can't rule out that Missy also collected the souls of Rory and Amy Pond Williams into the hive-mind data core when they died in their eighties. (If she did, I have a feeling that they would hace overcome the inhibitors just as the Brigadier and Danny Pink did.)
As this is a blog about the Toobworld Dynamic, (even though we've spent the whole day talking about 'Doctor Who'), we've got to assume that dead characters from other TV shows must have been resurrected as these Cyber-Zombies. And not just from British TV shows but from all over the world.
Let's put aside those characters who might still be alive, even though the actors who played them have passed away. Characters like Archie Bunker, Dr. Richard Kimble, Carol Kessler Bondurant, Tony Soprano, and Mike Brady. There are still plenty of others - most of the cast from 'Lost' to be sure!
Edith Bunker, Marshal Matt Dillon, Gary Shepherd, Lady Sybil Crawley, Bill McNeil, Pierce Hawthorne, Coach Ernie Pantusso, Chuckles the Clown, Danny Solano and Danny Latimer.
It's a safe bet that the skeletal remains of Bret Maverick and Nichols were raised up as Cybermen, but I'd like to think Jim Rockford is still alive.
I wish I knew more about TV from other countries so that I might add in characters from their programs......
I think based on that possiblity, we can expect to see "Missy's Cybermen" one day induced into the Television Crossover Hall Of Fame (probably in the Birthday Honors List.)