"Concrete plan" means a technology which satisfies all of these requirements:

1) demonstrated ability in a utility-scale plant

2) already economically viable, or projected to be economically viable within 2 years by actual process engineers with experience in scaling up chemical/electrical plants to industrial size

Yes, that's hard to meet. But the thing is, we've seemingly heard of hundreds of revolutionary storage methods over the last decade, and so far nothing has come to fruition. That's because they were promised by researchers making breakthroughs in the lab, and forecasting orders of magnitude of cost reductions. They're doing great experimental work, but they lack the knowledge and experience to judge what it takes to go from lab result to utility-scale application.