Makes too much sense
I've always thought that the best form factor for a tablet is the one that Asus pioneered with its TF-100 line -- a tablet with a detachable keyboard, the keyboard housing additional ports and a second battery. The TF is short for transformer. I own(ed) one, but it is now so old that it is too painful to use anymore.
To my great puzzlement, this format never came to dominate the world. It just makes sense: a proper keyboard, full-size USB, SD, and other ports, and a second battery that not only doubles the tablet's run time but doubles as the counter-weight to keep the tablet from tipping backwards -- and all of this optional.
Indeed, the battery lasts so long on the TF-100 series that I would use it to top up the charge on my smartphone. The one negative: ASUS used a proprietary charging connector, not the standard microUSB.
One Chinese vendor of tablets resurrected the idea, and so I ordered it. Curiously, the tablet had to be ordered separate from the keyboard. After the tablet arrived, the vendor told me that the battery-enabled keyboard was no longer available. I returned the tablet.
I recently got a 12" tablet with detachable keyboard. No battery in the keyboard, unfortunately, although it does sport two full-size USB ports. But here's the thing: the tipping problem. The vendor made the keyboard heavy (lined with lead?) so that the tablet would not tip; why not stick in a battery to provide the weight?