It must be exam-based. LI would be an obvious choice to run such a program. The program must have multiple levels. Students find this useful in that they achieve certain certifications as they progress. Training centers love the program because they can sell lots of classes.
Publishers love the program because they can create and sell lots of books.
For a Linux certification program to work, it, too, must have a series of exams. The exams must be difficult. It must be challenging to obtain the certification or the title will become meaningless. One of the toughest credentials currently is the Cisco Certified Internetworking Engineer. At the end of the day they send in an engineer to break what you built and your second day is spending finding the errors.