How do I set up a lets encrypt provisioned wildcard cert as the default certificate? Is this possible?
You mean this? https://docs.traefik.io/https/tls/#default-certificate
It does not look like you effortlesly can specify a cert from acme.json this way, but if you write a script to get the cert from there and put it on the file system that would be an option.
For what it's worth, you are not the first person, who feels that it is redundant to specify the same wildcard cert over and over again on all routers, I've seen this before.
So while I don't think that a couple of lines per router is a big deal, it's definitely an improvement that would be welcome by many.