A dialog for File->Merge

[micheus]

even with the current plug-in (...)

It's not a plugin. Just correcting the terms.
A plugin is something that I can make available for anyone that wants install it or not. This is an addition to a resource already in the Wings3d core - it will be available only if the main devs decide that. In this case, I just learned a little bit more about wings3d codes. (but, I don't care)

so I will just leave it and this discussion alone.

No problem. It's a brain-storm.

Just for use a simple (stupid) example about why to take care about the selection in a scene/object being merged, try to suppose that someone has a object library. In this case, a tree which the its base has one face selected for use when it is merged. So, we are creating a new scene whose we want put a lot of trees - we use the command .Put On. for that and it requires one face selected in the source object (in our case the base of the tree):
I used the traditional Merge for that.

oort, I think it'll become [more] confused.