Totally read my mind as I hold the same view. Designing the product in this way allows easy scaling while adding value to all parties. This alone makes the product better than most on the market today. Just following this simple concept of having the ability to add modules in a stacked manner would truly be a game changer.
Just spit balling here but lets assume the thing looks like a small rectangle. The main base would have X sensors. At the bottom would be push and slide rail where another sensor could simply be inserted.
Weather Flow comes out with a new sensor ~ No problem.
Just purchase and slide in that new gizmo you want which also keeps the initial price down for all. This would also avoid having to carry multiple sku’s for products. Just have a base unit and have the ability to extend its features simply by the push and slide tray topology.