I'm sure you (Jetbrains guys) must have considered this, but it's a thought that cropped up so I thought I'd mention it.
I've been using AppCode for some time, pretty much exclusively (forays into core data modelling and IB aside). Recently I (unusually) started a project in Xcode 5, expecting myself to pop over to AppCode for refactoring and testing, but I found that I preferred to stay within one IDE, even though I prefer (and had become more fluent with) AppCode. Something (attentional switching costs?) acted as a disincentive.
This gave me a bit of insight into the reluctance of many 'Apple ecosystem' devs to even look at AppCode, despite acknowledging its evident superiority for many purposes. Xcode is where these guys live, every day. It's a home, not just one tool amongst others (love or hate it). Most are going to stay there.
But many clearly acknowlege Xcode's weaknesses as an editor and refactorer. I am sure very many would part with good money for an add-on of some kind that would obviate these. A Resharper equivalent might do well. I realise Xcode might not have the necessary hooks available, but a reasonably compact standalone refactoring editor might work: something with AppCode's editing and refactoring features, but which worked well with Xcode as the primary IDE.
I haven't thought this through, and obviously there are a thousand complexities (and Xcode might be a hard partner to work with) but there it is.