Visual Studio 2013 is set to GA next month and RTM in November. Based on blog posts and mailing list messages, it seems that the WiX team is now struggling to meet their schedule of a WiX 3.8 beta release with VS 2013 support by Halloween and a final release by the end of the year. You can read more about it here and here. My guess is that with Rob leaving MSFT and the DevDiv embracing InstallShield LE that they aren't getting the VS team support anymore.
I've taken a look into what it would take and my initial impression is that there isn't any difficult VSIX work. A WiX setup developer with C++ expertise should be able to knock this out for them. Hopefully John Cooper will be able to step up as he has offered. If not, please consider jumping on the wix-devs list and see what you can do.
That said, I've done some prototyping using manual steps and have come up with some procedures to get WiX 3.7 working on VS 2013 RC. You can read those steps here.
I have also gone ahead and made all the changes needed for IsWiX to work on VS 2013 RC. Basically IsWiX interacts with Visual Studio in two ways. The first is a Tools menu bar AddIn. To make this work I simply update the AddIn XML to declare that I support VS 2013. No other code changes are needed as the integration is very simple and no other code changes are required.
The second interaction is that IsWiX leverages WiX infrastructure to provide two additional project template types. They are very similar to the WiX project types but more built out for a specific purpose. (Convention over configuration covered in my last blog post.) To get this to work I merely updated the IsWiX installer to locate the location of VS2013 and copy the project template zip files to the right directory followed by a call to devenv /setup. No other changes were required.
The problem is that if WiX isn't properly registered with VS 2013 then the IsWiX project templates won't show. There is no error per say... they just don't appear.
Hopefully WiX 3.8 will be released soon with VS2013 RC support. In the mean time I will be releasing a new version of IsWiX this weekend with my pieces completed.
Until then, my general recommendation is to never use project references and keep your installer projects and your application projects in different solutions. This way you don't box yourself into a corner if some of your projects are ready to upgrade and others are not.