I'll do my best to answer your questions in your initial post here:
1.) There is a way to insert your own door and window components. Within the plugin folder there is a sub-folder called "library" where you can place your custom doors and windows into their respective sub-folders.
2.) Yes, when you create a door opening on an interior wall (int-int) if you disable the advanced options the plugin will automatically wrap the opening in drywall.
3.) Bifold and pocket doors are both on the todo list. Bifold doors are more often requested so I will probably attack those first.
4.) The split wall tool was completed at the beginning of the year, the join tool and the stretch tool are both under construction. The join tool is almost complete, maybe I can get that one rolled out in a day or two. Be sure to check the changelog for development details:
http://design.medeek.com/resources/medeekwallplugin.pl5.) I'll have to think about the door trim question some more. I you more looking for custom trim profiles or something even more elaborate? Can you post a few examples of some door and trim configurations that you are interested in.