So I don't see this so much as an implementation question as a conceptual question. Are we considering the VPCs as sitemap components or something else, to me they look like sitemap components.
Conceptually, I think VPCs are components first and foremost. So they are responsible for parsing their own configuration.
Fact that it is being parsed now by outer TreeProcessor is a shortcut I took. If VPC creates own inner treeprocessing environment and appropriate node builder (PipelineNodeBuilder, probably), it will be completely independent of outer TreeProcessor.
(I think I'm repeating myself)
Vadim
