Input Overlays as I understand them are not ideal for this. I can see in the examples that static images are manipulated across the display, but they are still static images. Say I wanted to implement a timer that hangs out in the corner during gameplay - I would have to configure logic to swap out images for each digit of the timer every time increment. That's a bit much! I'm just looking for some way to add my own system text, similar to how the frame counter, fps, or memory utilization can be optionally displayed on the OSD.
As for the latter point, it seems like reaching out to the memory domains is something you can do in libretro according to the API, but I'm not sure how to set up a script that would assess memory state as it is executed - is there any kind of next_frame event or otherwise that could be used to fire off a script to check? There are numerous layers in the system, each with their own sets of capabilities, scripts, and events, so I'm not sure which layer I want to be targeting to get this kind of functionality.