Depends on what your laminate looks like, but it sounds like it should be fine. The only thing is that sometimes adding in real stone highlights how cheap the other countertop is so be prepared for that. But if you're considered changing all the countertops down the line, it should be fine to start with just the island (just know you may never get the same stone again because each slab is different).

I would recommend butcher block over granite if the laminate must stay. You may find that this is the perfect opportunity to tweak your layout and get better ventilation than a downdraft. I’d explore that first.