Sorry for not answering for so long - I had a lot of work with finishing the new version of ReaderSvg.
I have tried to use RenderTransform and it really does not look good. The ZoomPanel does not position the object correctly.
Also I have found a workaround for it - use LayoutTransform instead of RenderTransform.
The problem is probably caused by wrongly measuring the size when the RenderTransform is applied (the transformation is applied after the layout measurement. I will try to fix it in the next release - ZoomPanel will be the next tool that will be updated, but before that I must finish some other thing.
I am planning to add support for Sliders (so it can be placed inside ScrollViewer - and controlled by it), added auto ZoomPanel discovery to ZoomController (no need to use Binding in TargetZoomPanel property) and maybe some damping to the animated zoom that will make it appear more organic.
Andrej