Author here with several of the core team; we can answer some questions here. We also have a post on r/machinelearning for further discussion: https://www.reddit.com/r/MachineLearning/comments/9spw5g/p_g...
Out of the box, the meta-strategy is little more than simple-user defined heuristics (e.g., “if the the deepest candidate subnetwork performed best, try subnetworks that are one layer deeper than that”). However, the AdaNet framework is flexible enough to support smarter strategies as you mentioned, and abstracts away the complexities of distributed training (Estimator), evaluation (TensorBoard), and serving (tf.SavedModel).