yes, they have. It just costs a shit ton of money and is extremely difficult to get the suits to sign off on TWO full 'cloud services' bills. It generally doubles your cost and workload and increases your uptime by a couple hours/year, assuming you don't have bugs that affect one or the other cloud in your deployment stack.

It's basically a wash for almost all organizations for twice the cost and effort.

DNS

Not really. Your clients can random robin to connection points across providers and move write heads upon connection. If you worry about hard coding you can reduce the surface to a per-context first minimum contact point.