well, dialogs are difficult because of all the indirection taking place behind the scenes:
- Nasal wrappers create a PropertyList structure in the property tree
- events/actions/bindings are separate Nasal blocks
- the layout manager is basically PUI preprocessor
- then, there are the dialog handling fgcommands
- these "compile" dialogs from a property tree
Basically, the Canvas will improve the situation a little - but we will still need a Nasal module that supports the old dialog files, porting all these files would be a lot of work, which is why you won't see the format being depreciated too soon (I'd guess for another 3-5 years at least!).
Also, keep in mind the flexibility of the design - you could even use an I/O protocol (or telnet) to load a dialog and show it.