Good idea. I like the idea to add the resolutions from the SVG at runtime. The code is more simple, and it can work as well when adding images by code. The image is computed only once not every time it needs to be drawn as well.
I think it will be enough since anyways the wanted image size is fixed in some point, the Width property of the ImageList.
Edit: I changed my mind, Is compatible if just you can plug it and work with current image lists, no need of fancy IDE plugin, just adding images by code is good enough. And if we need to trigger some event in order to work, because is not automatic, no problem at all as well, just write some wiki explaining it and that' all.
Adding a single line of code OnShow is better than rethinking it again for the IDE plugin or because we need to load the images with code.
I prefer anyways storing in project options > resources the stuff, and load with LoadFromResource... methods.
Just my opinion, the code will be more easy to do and it will work with a bit of effort of putting a single line of code in the OnShow event.