As Google is about to introduce strict requirements for dev and foo TLDs, many developers will need to either always deal with certificates, install a local CA or use a different TLD.
It would be nice if we could customize the default TLD used by Local when creating new sites.
You beat me to it.
Google bought .dev a long time ago so this was a long time coming, but the HSTS issue brings it forward.
I’ve already requested this feature for the same reason 
While it was simple enough to change the TLD in Local, I agree the default needs to change.
I would suggest .local 
Probably, .local is not the best choice as it has a very specific purpose since is “a pseudo-top-level domain for hostnames in local area networks that can be resolved via the Multicast DNS name resolution protocol”: in some (maybe rare) cases, it may lead to issues.
.test seems more appropriate, as it’s a reserved TLD “not intended to be installed as a top-level domain (TLD) in the global Domain Name System (DNS) of the Internet for production use”: it seems perfect for the purpose of the local development.