So I'm in the process of redesigning the boards for the featherwing footprint. This should make them easier to use for feather adherents, as well as smaller in general. Keeping the ability to be wired standalone. These are in separate projects for entry into the current hackaday contest.

This has got my brain clicking that what I should really do is to put an ATTiny on the boards and run the code locally. This will make it much easier to use with non-Arduino platforms - save me learning how to do hardware interrupts on RPi for instance.

An ATTiny85 would not have enough pins even to drive a shift register and I2C and retain the reset pin so I'm thinking ATTiny841. On the 8 port board that has enough pins to drive the sensors directly, and it will fit in where the PCF8574 is on the feather footprint. For the 8 port I could either go with a more-pins ATTiny or go with shift registers and an ATTiny 841. As the sensor headers and the tristate buffers are all on the featherwing added footprint, there is lots of space to do that within the new form factor. And using shift registers allows for daisy chaining for people that want to use silly quantities of sensors. (like 16 isn't silly enough?)

Will have to bit-bang the shift register as the SPI overlaps the I2C on all the Tiny chips I'm looking at.

Naming is problematic 

maybe Octosonar3/8 and Octosonar 3/16 ?