Comment 96 for bug 1389723

@Jabiertxof - as mentioned on irc, I encountered a few issues with current dpiswicher.py. The attached diff is a partial rewrite (work in progress):
1) Scaling objects with 'matrix()' transformations produced incorrect results - I decided to make use of the functions provided by simpletransform.py instead of the custom method in DPISwitcher(). This simplifies composing transforms a lot.
2) Parsing SVG lengths from attributes now supports scientific notation (like the similar methods in inkex.py).
3) Page area of documents which have different units for <svg>'s width, height attributes (e.g. share/examples/text-on-path.svg) was incorrectly resized (fixed).
4) There is now basic support for text-on-path and <use> instances in SVG root (as siblings) to make sure scaling is not applied "twice" to instanciated elements.

Maybe you could test the diff [*], and we discuss details on irc?

[*] For text-put-on-path, you could test with Inkscape's own examples (share/examples/text-on-path.svg and share/examples/i18n.svg ).