Michael,

> There is some of that function currently in boolean union, when doing a union edges between 2 planes or between 2 pieces that are trimmed portions that share the same full "underlying surface" will be removed.

I wasn't aware of that boolean union's feature. Nice one. Thank you!!

> In the future I do also want to extend the Merge command to be able to merge selected faces together. Like I mentioned before though it involves a fusing together of surfaces, not just removal of an edge and it's a bit tricky to make it work well.

Yes, merge faces would be an awesome addition.

ed,

Yes I'm aware of Martin's script as well. It's a useful script but I think it does not do internal threads and you can't simply boolean difference an external thread because internal threads are a little bit different structure like this: