It should be fully Open Source project. If you want to participate as a developer or beta-tester or simply have suggestions, subscribe to Therion mailing list firstname.lastname@example.org. We (Therion authors) may participate in particular tasks and project coordination, but it's far beyond our time-possibilities to do everything.
The idea is following:
Labyrinth should use own, not text/command based data format. The best way would be to use embedded database like SQLite or Metakit. User should access data file only through Labyrinth user interface.
Must be portable to at least Unix/Mac/Win. Must support 2D vector graphics and OpenGL. C++ with wxWindows? (Qt would be preferable if there existed free windows version.)
Similar to other modern cave surveying packages (tables with customizable data columns).
2D map editor
Even more WYSIWYG and user friendly than XTherion.
(When therion supports passage wall modeling.)
Embedded PDF/SVG interpreter.