Now, imagine a vulcanised rubber form which is a really hard type of rubber. The power does seem unimaginable. Now, image the durability of Luffy in this form, it going to be insane and may be enough to even be able to damage Kaido. In this form may be Luffy able to fight on par with the Yonko.
But this gear of his will last for only a minute or maybe even lesser than that. And this form will damage Luffy’s body very much. In my opinion, Luffy is going to be unconscious for a while and thus won’t be able to move after using this form. After Luffy uses his ultimate gear, that is the gear 5, Kaido will be near defeat but will still survive gear 5. Now, I really don’t know what will happen after this moment. Maybe someone will appear and take Kaido down. People like Blackbeard come to mind. There are also lots of other possibilities on what might happen to Kaido.