Front wheel speed sensor retrofit ideas?

Can you read the vanes from the inside of the rotor? Like where you would read the lug studs?

You could also have the top inside edge of the rotor machined (outside of where the pads ride) with a series of notches or shallow holes.

Heck for that matter you could have your rotors drilled (vented) and read there

I'm planning to take the wheel off tomorrow and look around. I have one spare sensor that's the same as what is in my transmission I'm thinking would be good. I'm just not sure how much space I'm going to have between the knuckle and the rotor with the stock rotors. Feels like that is going to be pretty cramped, but I might be surprised. Not sure how the stock vanes are set up either, but will find out soon enough.

An optical speed sensor?

That's actually a pretty interesting idea. Wonder if you could clean up a surface enough to reflect where you want it and not where you don't so it would register well.