[quoting Hannafin's paper] A key problem with the trend in open learning, however, is that the raw number of "unique" methodologies has grown dramatically. ...if such approaches are to find significant place in training and education, we need better ways to distill the important aspects of diverse teaching-learning methods into a more powerful, versatile, and generalizable design model--akin, in impact, to generic ISD approaches.
Don't you think "distilling the important aspects of strategies that lead to open-ended learning" defies the purpose of open-ended learning in the utopian sense? Jenkins (1978) framework for evaluating questions about learning and understanding which I find very encompassing and relevant to any learning system, specifies four basic factors that one must take into consideration when designing learning environments: the nature of the materials to be learned, the characteristics of the learner, the learning activities, and the critical tasks to be accomplished.
Although this framework has largely been used to develop externally controlled learning or "instruction" (as you call it) in the context of traditional ISD designs, and although the definition of Open-Ended Learning Environments (OELE) inherently implies that "they are not designed to teach particular content, to particular levels, for particular purposes," I still think that, in order to create "an effective and efficient" OELE, you have to consider the particular context in which learning and understanding will occur and that is largely dependent on the four tenets of Jenkins framework.
Therefore, "distilling" the important aspects of "new methodologies" that create scaffolded learning into a "unifying" design system is not possible, in my view. And even if it were, it can only be realized in the very general sense which might not be prescriptive or useful anymore.
Creating an OELE is dynamic and evolutionary and therefore has to be constructed and negotiated "in context." Perhaps, this can be one of the unifying factors, but again it is only descriptive.
The idea of a "unifying system" in fact scares me, and I find it contradictory to the underlying assumption of "open-learning." At best, one can adopt a strategy that promotes open-ended learning such as PBL (problem-based learning) and modify it based on the characteristics of the learners, the nature of the materials or resources available for learning, the learning activities proposed by the strategy, and the nature of the learning task.