Hi Jakob,
Purr Data uses an HTML5 interface and the guis are drawn using SVGs.
There is also Pd-l2ork 1.0 which uses a library called "tkpath" for a subset of SVG functionality on a special tkpath canvas widget. Sadly, the original author of that library passed away and AFAICT the library hasn't been ported forward for more recent versions of tcl/tk.
As for tcl/tk-- it appears the next version of tk will do a one time conversion from an SVG file to a raster image. But that would not give you the ability to change any of the attributes on the fly-- e.g., rotating the knob based on input values.
On the other hand, I guess you could load the same knob SVG image multiple times and just substitute a different rotation value for each image loaded. Once loaded, you could switch out the displayed image displayed with the correct rotation value for the given input.
That's basically what I did for the little sprite game I wrote in Purr Data, and it worked pretty well both using tkpath and in HTML5[2].