A few items to keep in mind:
- Where do I want the intelligence handled? (FI's or ESXi) Either/Or but not both.
- Still follow best practices around keeping traffic separated and on different vNICs.
- Remember that the FI's are forwarding on the data plane up both paths A and B. With fabric failover, you will only utilize one side A or B at a time.
Lastly, test different failure scenarios whether it be upstream from the FI's or downstream, but ensure failover is working no matter the failure point. In short, both designs are valid, and I've seen both in production.