@JonB, both forum threads you've linked to are relevant to making the Xcode template work.
I'm hoping that I (or someone else) can put together at least a few bullet points for the forum, that will guide other people in the translation of scripts toward a working Xcode project.
Off the top of my head, what I perceived as "broken" pieces with Xcode 6.1 are:
a) support for 64-bit architecture, so you need to make sure you change the project settings to compile for non-64-bit for now. Not sure if support for 64-bit is coming down the road in Pythonista 1.6.
b) path to supporting files is not a trivial issue, so we need to figure out where .py, .pyui, images and other files are located. Ole's Textures directory seems to be visible from everywhere, so using any images and icons from that directory hasn't caused any problems on my end. For other files, using the find_bundled_files script can help you debug the location of your files (see https://omz-forums.appspot.com/pythonista/post/5234293353742336)
c) other than the path to supporting files, I've seen some slight differences in certain Views (e.g. height of a small pop-over) between iOS 7 and iOS 8. My solution has been to create two different scripts that deal with these two operating systems. Not pretty, but it has worked.
Note that my experience in making apps is very limited. I'm still waiting to hear back (after 2 weeks) whether an app I did with my daughter will make it through to the store - another simple drawing App. I'll make sure to update the thread that pertains to Pythonista-based Apps, should that be the case.
Hope this helps. Something more comprehensive will be useful for all.