The le1 is a space-limited device, only 16kb. So I am designing the dev board to interface with I2C sensors. Most nodes will take some measurement, temperature say, send it along and go back to sleep. Making a couple calls to the I2C bus takes up very little space, giving plenty of room for the network protocol and other housekeeping functions.

Only using I2C means that the larger versions of the le1 aren't really needed. No need to have a bunch of unused GPIO pins when you are only using SDA and SCL.

I haven't figured out how to deal with most sensor breakout boards coming with pullups already.