Note of caution: if qlmanage uses QuickLook SVG rendering, YMMV. I recently had to deal with SVGs that render broken in Finder but correctly in, say, Affinity or Adobe tools.
Rasterization feels sufficiently finicky that I personally would consider it part of designer’s workflow rather than automated conversion pipeline; but then some would say the same about raster versions at different sizes, so in the end it depends on what you can and want spend resources at.
If it does work for you, though, you could generate every size from SVG directly and skip sips altogether (but you should check both methods to see which gives you a better quality icon, at small sizes single pixels can matter and so it would depend on how qlmanage handles rasterization to different sizes).
Rasterization feels sufficiently finicky that I personally would consider it part of designer’s workflow rather than automated conversion pipeline; but then some would say the same about raster versions at different sizes, so in the end it depends on what you can and want spend resources at.
If it does work for you, though, you could generate every size from SVG directly and skip sips altogether (but you should check both methods to see which gives you a better quality icon, at small sizes single pixels can matter and so it would depend on how qlmanage handles rasterization to different sizes).