Myranda is both an unpopular sculpt, and ubiquitously fielded in Arcanist crews. She is also only available in Marcus's Crew Box, so an alternative sculpt will solve the issue of both the unpopularity of her pose and the cost of acquiring her for non-Marcus players. Note that there will now also be a demand for the Myranda model amongst McMourning players.
Personally, I would love to see an alt-Wendigo. That particular model is my least favourite in the Faction, an opinion that I seem to share with the majority of players. Everyone I know who has a Wendigo has sought a way to re-pose it so that it isn't permanently attached to that Guild Guard.
Arcanist lists containing two Sabertooth Cerberus (Cerberi?) are not uncommon. It would be nice if there were two different models available.
Alternatively, I quite like the idea of a female alt-Captain called Miss Chief, or something similar. He is a lesser-used model compared to Myranda and the Cerberus though.
As far as Masters go, I agree that it would be nice to see Ironsides in a more impressive pose.