Let me get this straight... If I buy 10 smaller "power banks" and plug them into 10 different wall sockets (or a 10-plug power bar wall socket extension).... I can fill up each power bank in very little time because they have 1/10th the mAh capacity required to be full as the one larger battery. As long as I don't blow my current fuse in the basement (what is it 15 A?) on that circuit I should be ok.
Now I take all 10 power banks with me, combine them into one unit... and if I need to charge my device.... I start plugging in each of them one by one... When one powerbank is empty, I plug in the next, and then the next, etc... until my device is charged.
... Or.... have it automatically cycle to the next power bank as it detects the current/voltage drop and sequence through all 10 of them until they are done.
So I think it is entirely feasible to do this kind of thing. And perhaps in the future even the batteries in the cell phones and other devices will be "massively parallel" instead of in series. Then you could charge up the devices much faster. But there will be more regulatory circuitry needed to "hand off" one cell to the next, and perhaps greater inefficiency due to having residual capacity remaining in multiple parallel cells as compared to the one single series cell.
Yes I agree with previous post which says that users may be confused that they can charge up the power bank very quickly, but yet still take a long time to charge their devices. Given that most people charge up their power-bank over-night, I don't see the issue being difficulty accessing an outlet to charge the powerbank. I think most people are willing to pay a premium to have their device go from 0% - 100% rapidly, not a power bank (which for the most part is usually not an issue having time to charge).