That said, Zen UV can already do what you want, technically.
The main limitation is that this can’t be done directly in the 3D View.
Blender’s selection system is quite restrictive: when you switch between vertex, edge, and face modes, it automatically converts the selection.
So you can’t, for example, select a polygon, then select an edge, and tell the operator: “stitch this polygon to that one through this edge.”
All these aspects — universality and Blender’s selection behavior — make it hard to implement such tools in the main add-on.
They would need to live in a dedicated add-on where users understand and accept those limitations and workflows.
And that’s exactly why specialized level editors can be so fast and convenient — they’re built around those specific constraints.
However, we’ve already received similar requests before, and this feature is now on our Feature Request list.
So there’s a good chance we’ll create a tool like this in the future.