When I first started writing IsWiX, I intentionally decided to keep it simple and keep the bar low for would be contributors. I decided to expose the in memory document as a raw XDocument to the designer (UI). This has worked out well but now I'm starting to realize what is really needed.
I've been getting irritated with InstallShield lately because I keep finding gaps in their automation interface. Now that I'm getting really serious with WiX, I've come to realize that WiX is practically lacking an automation interface. ( The .NET 1.1 CodeDomReader isn't very helpful.) WiX is a pretty decent schema and compiler but the fetish for NotePad++ has left some pretty big holes up the stack. While I understand my UI designers for WiX aren't for everyone, I'm pretty sure more people would be interested in a decent automation interface.
So I'm going to pause my development on IsWiX until I can come up with a good design that allows me to expose an automation interface for WiX separate from IsWiX and also work with Fireworks through some form of dependency injecting.
I have some technical debt to work off here. I'll get working on the automation interface so that the UI can follow. Course it would be really cool if the WiX team would write one themselves that way they could influence the authoring decisions made by third party tools.