Option to always use sidecar files for XMP

Question

Lightroom gives you the option to write metadata to XMP files, which is convenient if you want to share data with other programs (ACR, various DAM programs). In the beta versions, this data would always be stored in .XMP sidecar files, presumably for safety reasons. However, V1 writes the XMP data into the image file itself for those formats that support it (DNG, JPG, TIFF).
I would really like to have the option to *force* Lightroom to use sidecar files for XMP data, like the betas did. The current V1 behavior (embedding data) is quite inefficient for fairly common backup scenarios.
For example, I tend to back up all my raw files onto DVD after importing and culling. In addition I make a daily backup of all metadata that gets sent over the internet to a web server - a relatively small upload. What happens if I use DNG for my raw files and update something as small as a keyword? Indeed, *all* of the corresponding DNG files are modified, and because my backup software cannot know that only the XMP data has changed, all files must be burned to DVD again. If the metadata were stored in sidecar files, a simple, efficient metadata backup would take care of things.
To implement this, a simple switch in the preferences would suffice, and the necessary code is already there. The only possible problem is the occurrence of two files with identical names, excluding the extension. For this case, I can see four different 'solutions':
1) Force XMP metadata to be synchronized between files with equal names
2) Make an .XMP sidecar file for only one of the files (always the raw file, for example)
3) Update the XMP specification to specify what should be done in this situation (maybe include the file extension in the XMP data)
Reards,
Simon

Answer 1

Actually, I don't (notice the 'if' :)). And this is only one of the reasons. I just picked DNG as an example, to keep things simple and because it seems Adobe wants DNG to work well for photographers.
However, the same applies to JPG and TIFF images. I often end up changing details in the metadata after the image has been finished. For example, to correct the spelling in a keyword that has been applied to half the images in my database... Talking about a nightmare scenario!
Simon