Description: if multiple polygons overlap you can only select one of them. This is missing feature in JOSM too.

Solution is to implement "what is under here?" feature found in some GIS systems. Prompt user to select particular polygon that contains point requested by user.

Bonus points if it will order polygons in reverse layer level, i.e.:

1. house polygon
2. landuse residential
3. district
4. city boundary
5. etc

You may also query not point but circle with small radius (.1 m) - this will be more usable with bad input devices (touch screens, poor mouse pouting).

Please note that this functionality shouldn't replace current "select" function but add new one. Usually GIS systems use left mouse button as "select" and place "what under here" in right click menu.