To design a good keyboard case for the iPad Pro, OEMs must address two issues that can limit how well the accessory will work. The first (and easiest to address) is dealing with the physical size of the iPad Pro.
Keyboard cases must have a design that props the big iPad up in a stable way that doesn't allow the tablet to move around due to its size. Some sort of stand must be designed into the case to properly put the iPad Pro in a configuration that allows it to be viewed while used with the keyboard.
This is not as easy as it sounds given the height of the iPad Pro. The support provided by the accessory's stand needs to prop up the large tablet at an angle that provides a good viewing angle for the display.
The first two keyboard cases for the iPad Pro have a common trait that is likely a result of the viewing angle problem. The Apple Smart Keyboard and the Logi CREATE Keyboard Case both prop up the iPad Pro in only a single viewing angle.
This works well enough in practice but only having a single viewing angle is not optimal. Different work environments are better served when the display can be used in more than one angle. I'm writing this in such a case with the iPad Pro in my lap in a keyboard case and while it's workable it would be much better if I could adjust the viewing angle slightly.Designers can no doubt make a case that supports two or more viewing angles, but that complicates the process. Once a case incorporates multiple viewing angles in the design, the complication of how to make the Smart Connector work becomes an issue.
Testing the connection on the keyboard I'm using, it is apparent that the connectors on the iPad Pro must rest flush with those on the keyboard. Push back only slightly on the iPad and the Smart Connectors don't work; the keyboard is disconnected from the iPad Pro. The same thing happens when pulling the iPad forward just a little bit.
This makes incorporating multiple positions of the iPad Pro, even slightly different angles, a complicated process. Designers will have to come up with a way for the keyboard case's Smart Connector to swivel for connecting to the iPad Pro at different angles or worse, put more than one Smart Connector in the case. That would likely be an expensive proposition.
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It's probably not an accident that most keyboard cases appearing for the iPad Pro are going with the tried-and-true Bluetooth connection and foregoing the Smart Connector. The designers can build multiple viewing angles into these cases and not worry about the Smart Connector issue. There are no worries about keeping the connection flush with the iPad sitting at different angles.
That's not ideal as the Smart Connector works well. It provides an instant connection to the keyboard and eliminates the need for a battery (and charging same) in the keyboard. It's a shame it makes the multiple viewing angles difficult.
Keyboard cases for smaller iPads have incorporated multiple viewing angles for years, but they didn't have to contend with the Smart Connector problem. Perhaps OEMs will figure out a good (and economical) way to build a keyboard case for the iPad Pro that offers multiple viewing angles. We'll have to wait and see.