ModelMaker pipeline is not directly applicable, as segments may overlap and maybe non-integer (when fractional labelmaps are converted). It is also not entirely clear if non-visible segments should be taken into account for the joint smoothing.

Strong smoothing can be performed jointly already - using Smoothing effect's Joint smoothing method. The remaining smoothing during convertsion between binary labelmap->closed surface representation is only for removing staircase artifacts, therefore very little smoothing is needed. This very small amount of smoothing should not cause segments to pull apart from each other.

https://discourse.slicer.org/t/surface-rendering-of-many-segments/4044/9

Steve:
"The joint smoothing results are very useful in my opinion because they look more like real anatomy with smooth surfaces and no gaps between the structures. This is useful even if the conversion is only temporary."