Sure thing!

1. The main advantages of Threshold Components is to allow placing multiple seed points, and adjusting the locations of the seed points during the process. The underlying algorithm is otherwise similar to Region Growing. I created a new tool because I didn't want to interfere with existing tools, but it is certainly feasible to add these features into the existing tool (if you think they would be useful).
2. Pruning removes protuberances only of width 1 pixel. The rationale for pruning is that Morphological Opening, even at the smallest radius, ends up deleting much of my segmentations. Pruning cleans up the noise slightly without affecting the wanted regions. (I agree that the effect of Pruning is small - it is meant to be coupled with Thinning to skeletonize the object first, but that would be even more destructive.) There is much room for a middle-ground that is gentler than Opening and more forceful than Pruning.

Added another commit that fixes a minor bug in segmenting for Deformable Clipping Plane View; the item number in QListWidgets does not always match the label number in the Clipped Image if there are empty clipping regions (items not equal to 2^n, where n is the number of clipping planes). However, the label number is always monotonic increasing with the item number, so this fix uses Histogram to map the item number onto the label number.

I've sent a pull request adding the extensions I was planning. The summary of changes is: