That's addressed in the article: "We purposely don’t employ dynamic IPs to retain multi-cloud deployment capabilities and prevent vendor lock-in with one platform."
Why not have the machines presented to the clients or other interfaces by a virtual IP from an application delivery controller such as F5's BigIP or similar? And then remove the dependency on static NIC's on a virtual appliance?
Seems counter intuitive to run virtual appliances on static addresses if it can be avoided.
That still makes no sense. AWS and DigitalOcean both allow for static IP addresses that can be migrated between instances. There's no reason for crazy in-place upgrades.
I'd hazard a guess that the cost of moving IPs would severely outweigh the cost of switching VIP implementations, in terms of preventing a move across providers.