I have just played with Kdenlive SVG support. What is the official status of supporting such complex format like SVG? What about advanced features like filters (blur is essential for nice behind-text shadows) or even animations, javascript?

I have just played with SVG. I was most interested in filters.
What I found is - it depends how you add the SVG to the project.
1) SVG is added to project straight as "clip", then filters are supported! Great news. I was able to create text title with natural shadow or outlining.
2) SVG is added to title project through "title clip". Now filters are NOT supported, not in the titler window not in the rendered output.
The second way has the benefit of editing options - resize SVG, reposition, add more stuff. Quite useful, but missing blurred shadows is a usability blow.

My guessing - kdenlive titler uses a QtSvg module, which supports only "SVG 1.2 Tiny" (no filters and static only) but MLT uses something more powerful! But what?

I experienced one a noticeable green "halo" (partial outlining) around my yellow text when put on darker background (composite effect). It is always there, even when using a simple SVG, (just a plain text, no shadows, no filters, just the text) in both composite window and in rendered output too (slightly less). It is not SO bad, though it is an artefact.

Is SVG templatable? So I can have one SVG template and just change text, ie text substitution, or even a color, or image name (like bitmap part of a SVG)?