SVG Gradients can be handled by primitives and are supported by all exports, but are not yet available e.g. as gradient setting for draw objects (supporting multiple color stops and other stuff). This is planned, and ODF already contains SVG gradient definitions as allowed statements.
The idea is as soon as this is available to break objects with SVG gradient fill to their simple geometry and setting the gradient as fill style. As long as this is not available there are two alternatives:

(a) Create bitmaps
(b) Create single-colored polygons clipped against the original geometry which reassemble the gradient

Both have pros and cons. The main reasons for using (b) are that it stays vector graphic and thus preserves better quality on later processings (exports). The cost is more geometry. The main disadvantages for (a) are the loss of quality and the need to 'guess' a good resolution for the bitmaps.

Thus this is best solved when we actually have SVG gradients in the core. Addendum: Currently the break still converts to metafile and then to draw objects - a direct converter from primitives to draw objects in the core is still missing and would also be needed first to avoid double work.