I think you are talking about two different issues: one is having two separate pins for rain sensor and flow sensor (and this has nothing to do with OS vs. OSPi, both of them have enough number of pins, but the enclosure has only one sensor connector); the other issue is having a common set of I2C components shared between OS and OSPi. For the second issue, all hardware platforms (Arduino/OSPi/BBB) support I2C, so you can definitely connect any I2C component to any of them. Also, the main reason behind the Unified Firmware is indeed to have a common piece of firmware that can compile for all of them. Regarding ADC: since Arduino and BBB both have plenty of analog pins, there is no reason why not to make use of them. The fact that RPi doesn’t have ADC is really a downside of it. Regarding pulse counter: all three platforms use Interrupt to handle pulse count, which is already supported in the Unified Firmware.