I've been pondering this question too. NTP is a very important Internet service and it's great that folks are looking for a more secure alternative to tradition

I've been pondering this question too. NTP is a very important Internet service and it's great that folks are looking for a more secure alternative to traditional ntpd. I'm not sure if NTPsec is going to get there or not. The best alternative out there right now seems to be Chrony. But it hasn't had nearly the inspection and usage ntpd has had, so it's hard to know for sure about its security. ntimed was also looking promising but seems stalled. openntpd doesn't keep time very well and systemd-timesyncd isn't really an NTP implementation.