I actually think Zoro could do extremely good against Kaido if both stood under proper health conditions. Considering how he managed to stop Hakai for a while despite not standing in his best asset and how that was equating to tackling the energy blast of two yonko combined I bet he would probably be able to withstand several strongest Kaido attacks with his defensive output alone and he also displayed a very compelling attacking speed when finally unleashing his CoC in particular, enough to seemingly blitz him, or at least the panels made it look like Kaido didn't have enough time to launch his attack prior to Zoro's Onigiri. His Base speed should also be pretty consistent, I doubt there's such a large margin Kaido would start to let's say dodge his Shishi Sonson attacks. Overall I think that Zoro vs Kaido is already a fight all to watch.
That doesn't mean Zoro is necessarily ready to stand on yonko level, I don't know how many attacks it would take an healthy Zoro to defeat Kaido, probably less than a few dozens like some pessimistic users predict, but if I had to make a guess Mihawk still being likely 3 opponents away suggests that Zoro is probably still not pushing him past mid difficulty. Perhaps high end.