Kodi always outputs progressive, so if you have PAL 576i@25Hz media it will be converted to 576p@50Hz by rendering each interlaced half-frame to one progressive frame and your output device should support 50Hz modes. I'm not entirely sure what then happens in the kernel DRM layer if you force the output to an interlaced device, but I'd assume it must be converted and I'd expect 576i@50Hz to be the result not 25Hz as I doubt the DRM layer is configurable or smart enough to detect the progressive output could be (re)packed into 25Hz.
NB: These days Kodi is written around the assumption the GUI is always 720p or greater, so while you can get output on a lower resolution display, the GUI layout and will not be optimal.