These days all good players will resume playback from the last playlist when closed. I want to switch between playlists and have the playback resume from the last point of the last video. I'm not talking about opening the app and resume the last list, I mean switch to random playlists and each playlist starts where I left off.
https://github.com/tomek-o/VideoPlayer - this is simple GUI for mplayer. Playlists are stored as JSON files in application subfolder, each playlist contains information about last played file and position inside it.
Most functions are accessible from context menus - one on the playlist tab (creating/renaming/deleting/hiding playlists), one related to playlist entries. There is single executable (1.2 MB) if you already have mplayer and 7-zip file with mplayer included (31 MB unpacked). Application is mostly controlled from keyboard, following default mplayer behavior.
It may not be adequate for thousands of playlists though and there is no voice control.