Does this support multiple .pde/.ino files in a single project? If so, do any errors point back to the correct original source code lines?
.pde / .ino files are considered as .cpp files and are natively supported.
However, some extra code is required and should be added:
// core library
// needed here
// separate main.cpp creates conflicts
for ( ; ; ) loop();
Defining a separate main.cpp with main function or using the main.cpp provided by Arduino / chipKIT resulted in duplicate declarations and loss of code-sense.
Function main is the compulsory entry to the code to active code-sensing and all other niceties.
I haven't added yet a routine to check there's only one .pde / .ino file.
Xcode is poorly documented but has automatic features supposed to make developer's life easier
. Xcode doesn't support plug-ins, so I'm afraid I can't go further... unless a white knight comes to the rescue!
Would you like to consider NetBeans instead? It's cross-platform and has an open architecture for plug-in. Combining your expertise with Visual Studio on Windows and my tests with Xcode on Mac OS X, we could do something really nice.