Yes, yes, yes. I agree with this suggestion.
The reason I need it is because WIX is kinda a pain to get set up right if you're not experienced with it. There is one main reason I want WIX files - because my clients ask for them. I have a major client that needed an installer, I built one using AI, they came back later and ask me to make a WIX version. The reason they wanted WIX instead of AI is because WIX files can be easily incorporated into continuous integration systems so every code checkin results in a full build with installer. Because they use WIX for their other stuff I couldn't just tell them to buy AI and figure out how to integrate it into their build process, they never would have done it. WIX files, being just XML, are more easily modified on the fly during a build process so you don't have to keep X copies of installer projects due to minor variations in the resulting installs. At least that's what I understand about WIX, I could be way off.
Also, AI is SO easy to use and there aren't any decent WIX UIs as far as I've seen. I tried reading through the docs to create my own WIX file and my head started to melt. It was painful having AI just sit there while I wallowed in complicated WIX documentation. Since AI and WIX both target the Windows Installer it seems like anything AI can do should be translatable to WIX. Also, there might be things WIX can do that AI can't do as easily yet. If I encountered a case like that (I haven't ever yet) it would be nice to build 99% of the installer in AI, output to WIX, then tweak the WIX file.
Please, please, please.