I think an autosave feature would be nice to have in general, but I also really like your idea of using Tiled as a tool to keep track of the explored area and to stream that using OBS. Instead of a plugin, possibly the "tmxviewer" application could be used to render the map, if only it would automatically reload the map file on changes (which is something that could be implemented). Of course a plugin could add functionality that would not be possible with an external application.
I've opened an issue about an autosave feature.