I like the concept, but there is an inherent difficulty in this that would have to be overcome (and it’s not isolated to what you are suggesting, I’ve experienced it in what I’ve tried to do).
What I’ve learned about all my work on the Maslow is that you can’t improve the accuracy of something unless you can measure to something better than what you are trying to achieve. For instance, if your goal is accuracy to < 0.5 mm, then you have to be able to measure better than that to maybe at least 2x times better based upon a gut feeling, but maybe much more is needed… I’m sure if I did some research and read some books on the topic, this has been figured out already.
So, with that said, if you want to put markers on the board that you move the router to and compare actual chain lengths vs. what you calculate, you have to place the markers extremely accurately. Across a 4x8 sheet of plywood, placing the center of a marker down to no greater than 0.25 mm accuracy will be incredibly challenging in my opinion. If you look at my work here: Optical Calibration Demo and Three Hours Working on a Bug you will ultimately see I used a 4x8 printed pattern on a banner. That pattern isn’t perfect in itself because the printer the company used isn’t perfect. So then what do you do?