While I agree with getting rid of at-will policies, I disagree with one part of your idea. Why would I ever want to indenture myself to 5 years with the same employer? How would unions be handled? How about strikes? What about health insurance benefits?
Frankly, unions already solve alot of the problems with at-will employment, and should be protected by law rather then systemically stripped away.
Friend, your guild idea already exists. It's just called a Union in the current day. Many trades already operate this way, from the Carpenters Union to the Iron Workers Union. There's even a Teamsters Union. The different name doesn't change the work they do. White- collar hand much less representation with collective solidarity, but that can be fixed by starting a Union at your local work place. I won't tell anyone it's easy, but it's worth putting in the work. A great example is the Starbucks unions that have popped up in the last few years. The reason you don't see more unions is because employers are terrified of them, and want to continue to freely exploit the workforce through fear.