The SVG to be displayed exists in an external file on the server that Drupal can see.
I've been thinking about features that would be useful in such a module. The most important feature is that it should do everything possible to display the SVG. In some cases this would mean that substituting a PNG graphic is acceptable. In other cases maybe it could use Batik or one of the Flash-based SVG viewers that some people are working on. If none of these is suitable then the module would have no choice but to show error text that gives the visitor some idea of what they can do to make their user agent (browser) show the image.
Since I'm on the subject of compatibility, maybe it would be worthwhile to allow site authors to do some user agent sniffing or feature detection. Then if an implementation is known to not support an essential feature of the image being displayed, a fallback could be attempted. I know it's not a pleasant option but I'm trying to be purely pragmatic: I want this to make life as easy for website creators as possible.
As an advocate of SVG, I like to make demos. I need to show the source. I intend to add a tab to display the source. This should be nicer than the ad hoc way I've done it in the past. Sometimes I used prettified XML and sometimes just plain text. Demos are better when people can mess with them. So another feature that would be nice would be an edit box where the source could be edited. This is a little more challenging given that I want to work across browsers but it should still be doable.
The source and editor tabs aren't useful to everyone of course, so I can add configuration for those features. Either in the module settings or I could make it part of the svginlay tag that I use.
After all that work I have to consider how such a module should interact with other popular modules. Are there any APIs that should be exposed? Is there a way to integrate with the CCK or Views modules? Still lots to decide and lots to build but I think it'll be a useful module. Anyone with suggestions, comment here and give me ideas what people expect.