CNC.js also has the ability to add plugins, although it’s a bit less automatic than octoprint.
There are also pendants, which also look sort of like plugins to me :).
It seems to me like there are at least two issues with that:
What features are you going to use for the 0,0? The lower left corner of a workpiece would be pretty good, but I am often cutting things out, so a little inside the corner is my preference. But then some designs might be the center or the upper right.
Once you know what you’re looking for, being able to find it (assuming you’re starting close) shouldn’t be too hard from a CV standpoint, but you need good conditions for CV (good lighting, focus, exposure, some actual features). I don’t think a sticker would be necessary, unless that’s what you’re planning on using to determine the 0,0.
I think it’s cool, but I’m not sure it’s that useful. There was a PCB milling machine at my old work that had a camera system. It had a vac table for clamps and it would look for each corner and adjust for skew. I don’t remember how it determined Z.