Stanford is just trying to cash in on people by having their cake and eating it too.
They want to charge 20k, but not let anyone have a chance of further advancing to complete a real degree, no matter how excellent their performance in this program.
The reason they do this is solely to protect their brand and exclusivity. They already offer online degrees but the acceptance rate is just as limited as the on campus program.
Yes the learning is important, but so is the credential and a certificate doesn't even come close to a degree in the job market.
Stanford should pick one:
1) Charge Stanford prices, scale up online, and let any student who can do the work pay tuition and earn a degree.
2) Charge lower prices for certificates and continue to artificially ration real degrees.