I am afraid I don't have better information on when but some anecdotal information about the state of it. I have done some limited testing and research for our

I am afraid I don't have better information on when but some anecdotal information about the state of it. I have done some limited testing and research for our own internal Root CA I got the impression it works nowadays. I have not gotten as far as testing it in production but based on testing Safari and Chrome in https://nameconstraints.bettertls.com/ https://nameconstraints.bettertls.com/ and creating our own name constrained cert and testing it with both OS X Curl and Linux Curl (OpenSSL) I am still of the impression it works. Most other people seem to be sure that it does not though (for example in this discussion and here https://security.stackexchange.com/questions/95600/are-x-509-nameconstraints-on-certificates-supported-on-os-x https://security.stackexchange.com/questions/95600/are-x-509...) so I am not sure if I missed something or if people are just not up to date.