I will say, if people buy it, I think BCS is more than willing to go deep on character selection. Their plans for Penny Dreadful were ambitious, before that got scuttled by the show's surprise end.
I'd argue that the Penny Dreadful cast felt more like the were all "main characters". Look at this pic:
All of them have a distinct look and some of them a certain amount of star power. No two of them look the same, and in-universe they all had their various subplots going on. Then you've got the fact that characters like Dorian Grey and Victor Frankenstein (alongside his Monster and the Bride) are part of the world of literature, not just from a tv show. Vanessa herself has quite a couple of outfits so that they can make multiple figures of her. Hartnett's character has the Werewolf aspect as well. There are more incentives to go deeper there than a semi-popular BBC show whose main draw is the main character. Yeah, a lot of people tuned in PD to watch Eva Green get her **** out, but some tuned in for the Victorian Feel, others for the Literary characters; etc. PB started as basically British Boardwalk Empire crossed with Sons Of Anarchy, so you got into it specifically if you liked Crime Dramas so much that you'd watch anything. But it became a hit because all the girls were salivating over Cillian Murphy, who carried the show, and because of Hardy dropping in (who's stayed on for so long because he finds the part amusing). It's a similar case with HoC being carried entirely by Spacey and riding the coattails of the first few Fincher episodes. And, like HoC, the writing's gone to hell. The scene with the Nuns in S5 is all the proof anybody would need. But, in contrast with HoC, it keeps getting more popular.The show's done well, yes. I see pics of them up in the walls of most barbershops and even housewives watched it. But all the pics are of Tommy & Arthur, all the housewives are watching because of Tommy, and personally, I had to look up the names of the other brothers. Anectodal, but there you go.
Peaky Blinders is primarily carried by Tommy, with Arthur as the "underground favourite", and Alfie as the fun guest star. All of the Peakys are merely the "minions" of Tommy/the "Overlord". Tommeh is the main character, which is why anyone interested in the property will get him. Arthur has a different haircut, the mustache, he's the "bulldog"; there's enough to differentiate him and make people wanna buy him. But Michael, John and Finn are just the same outfit but with characters that I don't see anyone spending 200$+ on. Polly? Grace? Ada? That whore Tommeh ended up marrying? The black guy? The black guy's kid? The black guy who ****ed and sucked Ada and Tommeh is a-ok with it, when two seasons back he was racist against Italians for daring to **** the whore whom he ended up marrying, even though he goes on and on about how Pikeys are mistreated while also being a degenerate criminal? I don't see them getting made. Yes, the show's done well. But "boy, I'll sure drop 200 pounds on a supporting character who's jsut there" big? I don't think so.
If Tommy does well, they'll make Arthur. Then Alfie, who has a distinct look and is played by Tom Hardy. If the line is still going strong, they'd do Aberama because he's got a pretty unique look too, compared to the others. Then Luca, since he could appeal to Mafiafans and is played by Brody. Then, if they're brave enough to make a figure of the Leader of BUF, Mosley. I heard that Brad Pitt called up for a role because he's a fan of the show, so if he ends up playing someone, they'd make that guy too.