7. Dress Of The Times
No matter what Capaldi dresses in, there's definitely something I'd like to see his Doctor do more than any of the other Doctors have, and that's dress appropriately depending on the time he's in. Hartnell's Doctor did it a few times like in The Romans or in The Gunfighters (and likely a few others though I'm not as versed in Classic Who as I am with New Who, forgive me). So that's something that'd be nice for Capaldi to do. Imagine Capaldi running about in Victorian getup with the Paternoster Gang, then his regular outfit for the next few episodes, then a toga for ancient Pompeii, and a wig in the episode after that when he visits the 1700s. It'd certainly be more fun outfit-wise, with a costume of the week.