What the title says.
I could imagine this one, but then only for the available output streams of the plugin itself. so mono plugins would only allow one fx chain set, because there is only one stream.
Some sampler plugins allow multiple output channels which could benefit from separate fx chains for each output.
This would then require a rework of the outputs and routing section to allow fx chains (which imho fits better in the center frame of the instrument area rather than the left side in the plugin panel.)
I’m not sure if that is easy, but for the samples the layout already exists.