I think that one of the revolutionary things on this is the I2C and power connectors available under the cover. It's the start of things becoming modularized. You want IRDA, get the back cover that adds it. You want what's next after NFC? Add it. You want a hardware slide out keyboard? Add it. You want an eInk back like the Yotta phone? Add it. You want a full USB port? Add it. All of those things can be done over i2c.

Random List of i2c components: http://forums.parallax.com/showthread.php/99160-List-of-I2C-...

Spark Fun: https://www.sparkfun.com/search/results?term=i2c&what=produc...