Licence is MIT / Apache, of course.
EDIT: of course the relicensing is the problem here. Alas we’re in an all-time low interest in Free and Open Source politics, ideologies, and organization so the Big Evil Corpos continue to do their thing, one cog per time.
The latest version of NTP is 15 years old, and implementations are expected to be compliant. There is no risk of embrace/extend/extinguish from licensing here.
Open standards are better than copy-left licenses, IMO.
The money influences the standards and look at which licences the big pockets are pushing. Sometimes I can’t stand the naivety.