I went to a high school with no grades. It was great. My peers and i wanted to learn and we did. And there was no grade hype/complaining/competition. It works.
The reality is as humans we love to learn things. Focus providing an environment that delivers that and the motivation is not a big issue.
1. How does one know one mastered the material? I've often thought I knew it, but found out I did not.
2. How does a college know one mastered the material?
3. Even when doing things one loves, there are always some boring things that need to be done, too.
BTW, in learning to program on my own, I later discovered there were yawning gaps in my knowledge that were conventional knowledge taught in CS classes. It was embarrassing.
The reality is as humans we love to learn things. Focus providing an environment that delivers that and the motivation is not a big issue.