About the longer grove cables ....
Should be nice if you can offer the possibility to join two or more ... Shields or grove sensors ... Into one only device
Alex Bruski commented
You can extend grove cables easily using the I2C bus expansion. Just plug in two grove cables.
I like your idea of allowing sensors to be ordered with multiples of two on one board when each of the sensors just uses one control line. They make Grove Y cables that allow you to connect two sensors to one Grove port on your Grove Shield, but that still leaves the extra real estate being used for the two sensor boards.
For I2C controllers and sensors, it would be cool to be able to configure and select multiple devices on one I2C board. This would be even easier to implement with the use of my idea to have I2C sub-addresses.