There are very few companies that are willing to purchase network gear from two different vendors and run two completely different network stacks.
Management would be a huge pain in the ass... but it would be doable.
We are a large regional ASN in a tech heavy market and run 3 different vendors of DWDM platform and both Cisco and juniper in the IP core. Diversity is good.
Plus a third box for testing firmware updates before you touch the live ones.