Thanks for your enthusiastic compliments!
1. I am considering a feature based on the filters pane, where you would apply some filters to every person in the database, and see a flat list of persons matching the criteria. There would be a few more criteria, e.g. the number of parents, or of partners (which may be different than the number of marriage events that is currently available). Would this match your request?
2. On a descending tree, all spouses of each descendant are already shown (with a branch for each child the spouse had with this descendant). If you want to see the previous/subsequent partners of these spouses, and their children (which are therefore not descendants of the root person), or if you want to see previous/subsequent partners in an ascending tree, use the "other family members" option in the person description pane; they won't appear as leaves of the tree (and won't have any branch displayed), but they will be mentioned in the details of their spouse.
3. The tree grows in a single direction, either ascending or descending, and branches only show ascendants, descendants, or spouses of descendants. I have no plan to change that, as this would become really very complex.
4. comparing (and merging the differences) databases is complex and beyond the scope of this app.
Updates are and will remain free; users are however welcome to make additional supportive purchases at any time from the application menu :-) (you can't currently purchase multiple times for the same amount, but you can choose a different price).
Thanks!