more accurately, they don't support the common standard methodologies for transferring zone data between primary and secondary name servers (like NOTIFY, AXFR, etc).

there is nothing stopping you from having Route53 and $others as NS records for your domains. You just have to make sure they stay consistent. Apparently from the linked discussion, there are people offering scripts and services to do just that.

Thats why you should have a different domainname

githubstatus.com instead of status.github.com

You could even through the domain on a free DNS service.

Maybe not, but you can store your records in a local place and push to both.

That's one of the reasons I setup a git -> Route53 setup at https://dns-api.com/