@Samu Wow Samu, thank you for your incredibly thoughtful reply! I've put "The Cabinet of Doctor Caligari" on my watch list
I agree with your thoughts on style. I'd never consider changing my style to suit a market and I have seen plenty of picture books that strike a sombre note. Many of my favourite picture book illustrators that fit this description seem to be European and most of them seem to be published by OQO Editions. In fact it wasn't until perusing bookshops in Paris and stumbling upon such illustrators that I ever considered illustrating for picture books. So I agree, there is definitely a market for it but I may have to move to France 
I also remember liking darker things as a child. I was completely bewitched by The Labyrinth, The Last Unicorn, and even Puff the Magic Dragon - possibly the saddest song in the world 
I must admit I am confused by your confusion
There is certainly plenty about this illustration that I am proud of but at the same time I genuinely don't know if an art director would look at it and think it is of a "publishable standard". And I also genuinely don't know what they would tell me to change or improve to get it up to that standard (apart from what has conveyed on here r.e. expression, etc).
Thank you again, Samu - I really appreciate you taking the time write so passionately on something I also feel very strongly about - we are of the same mind 