Okay that explains then: Apple needs to be a bitch about things again.
if lithium batteries weren't so problematic when overcharged you could float-charge everything pretty efficiently, then you wouldn't even need a management system.
Our current way of doing things is probably here to stay, though.
A data channel isn't a data channel. USB is designed to be widely used by many industries, as such the standard has provisions for many use-cases. A battery data channel is only for the charging equipment to communicate with the battery's chipset a limited amount of parameters. The data being transferred is incredibly limited, and can thus be sanitized easier when compared to USB.
A protocol designed in such a way would also be easier to test, as the scope of vulnerabilities would be much more limited than a general purpose data channel.
Regardless, it was merely a possible answer to
> If you disconnect the data pins, how can any device (apple or anyone else) get more?"
and really wasn't meant to be a valid product or concept. Just a fleeting thought.
The obvious drawback would be that such device connected to charger without current limiter would burn it.
Then again I just burned a charger that had multiple sockets by connecting Samsung Galaxy Note 3 and iPad2 to it. It advertised via data lines capacity for 2A charging on all five USB sockets, but had total capacity of just 2.5 A.