long-time Inkscape user here, looking to get into coding for it too.

I created this really simple extension for setting CSS classes on elements.
It has an option to clear inline styles of the elements, so that the css class would have an effect.

It is useful when having numerous elements that repeat or have the same styles.
First, select a correctly styled one, use "Merge styles into CSS".
Then select the rest and use "Set CSS class" to apply the new style on them.

I am aware of the extension posted on the forums that sets classes, but having to manually clear styles after is a bit of a pain, so not completely usable for my case... and it's not in a code repository, so no way to contribute.

I read that in GSoC CSS handling will be improved, which is awesome!

Hope someone finds this useful.