Any chance to add Hell To Pay and Perdition Gate, to this amazing tool ?
Those aren't official (or effectively-official, like Romero's maps) releases, so no. But if you look at the data inside the doom_complete.pk3 you could add support for those as new episodes without much difficulty - you could copy the mapinfo\doom2_levels.txt and have a decent template for a doom2-shaped episode, and only need to change a few things such as level names and music tracks.