SQL LB

I'd suggest a slightly different approach to improve redundancy. I'd build two Performance (Layer 4) Virtual Servers, one for each cluster. However, I'd use two Pools and Priority Group Activation. In each Pool, the intended cluster would be specified with a priority of two and the other cluster IP configured with a priority of one. Set minimum members to one. That way, if a cluster went down, traffic would switch to the other; but only if the 'primary' is down.

As I assume there is no need for Persistence, when a failed cluster comes back up everything would revert back fairly quickly. Using OneConnect for both would also greatly reduce the number of active connections each cluster needs to deal with, probably saving a fair bit of memory usage.