Although I too echo the sentiment, Inkscape isn't currently set up for such things. It its, however usable for UX design, and is used by the GNOME project for mockups, etc.
It's doubtful in the near future Inkscape will acquire the many many conveniences that UX design programs have.
It's not impossible, but currently our developers are working on making Inkscape better at what it already does to provide stable releases for the future.
That said, there's nothing stopping interested parties from creating a UX design branch of Inkscape to explore the possibilities.
It's just we don't currently have the dev power necessary to undertake a major expansion like that.
Just adding some concept of "flow" would be difficult enough, and would likely require different dialogues to be usable in the same way UX programs do it.
You might also consider experimenting with extensions, which, say take svg objects on canvas and export them in some particular order along with an HTML file with some fancy css and javascript to do your animations and flow transitions.
Building that externally would offer a way to do UX in Inkscape without modifying (or cluttering) Inkscape's current user interface.
To be sure, it's a great idea, and I think if you have the time and means to learn some Python to make this extensions (which Inkscape already supports to some degree), you could potentially make some really great add-on tools to help people make more fancy UX stuff in Inkscape.
As far as adding page templates for different devices, that's actually something we could do fairly easily, and would be a nice to have for many developers who make mockups in Inkscape.
1. svg to code conversion - Difficult, but could be done as an extension for Inkscape or completely outside of Inkscape.
2. library management for projects - Probably not doable currently. However Doc and Jabier were working on the ability to link in svg files, so you could just use a file folder for your shared library items. Changing an item linked would change every instance of the svg in the file. You could also do what I do and create off-canvas shared objects (what I call a "super-template") and use clones of objects from that to arrange your designs.
3. parametric design convention - Yea, not really anything to solve that issue yet. More css is being integrated into Inkscape however, so it's conceivable that this will be less of an issue to accomplish in the future.
4. standard templates - I intend to make some of my "super templates" available to the public soon. These are different setups for making different kinds of things, from business cards, which auto-update an exportable preview of front and back, to website templates for making quick mockups. These simply use Inkscape's built-in features to work, so no code needs to be added.
5. animation - Yea, nothing at all yet. It's not that it can't be done, it's that figuring out a good UI for such a thing in Inkscape is a major undertaking. It may be possible to write a javascript program which handles the animation bits of svg components exported from Inkscape, in some standard way.
Thanks for sharing your thoughts and ideas, and welcome to the project! :)
-C