Due the elimination of the ion-exchange membrane I think the life of battery will be more as compared with the Lithium-ion batteries, but again the life will be limited because of the electochemical reactions at the electrodes. The article is not discussing about the life of the battery which is an important parameter in comparison of batteries.
The researchers primary purpose in eliminating the ion-exchange membrane, was to extend the lifetime of flow batteries, which they now claim to have achieved. However, long-term tests have yet to be performed on real membrane-less flow batteries to determine just how long they'll last.
Yes you are right, and from the architecture of the battery as explained it seems that this batteries will be surely have more life time as compared to the batteries we are using today. But will have to wait for the actual results for the exact figures.
Yes there are many ways to store Big Energy--my favorite is compressing the air in unground caves during demand lulls, then bleeding it off to generate electricity during demand peaks.
Smaller versions are possible--since their protype is small enough to handhold--but these researchers had the primary goal of meeting the $100 per kilowatt mandated by the DoE, which is the break-even point for grid-scale deployment.
Maybe pump it up-hill at night when demand is low (and energy is available for pumping) and flow it back thru the turbines during daytime peak demand. BTW Niagara Falls will soon have more generation capacity due to a "big-dig" to increase flow!