I’d tested earlier and got the useless 9.x “add events” behavior when tapping on our special hockey calendar feed:

webcal://www.mnspecialhockey.org/ical_feed?tags=1768556%2C2152725%2C2838825

Today from iMessage I got “subscribe to calendar”. Added as new subscription source to Calendar.app. 

Feed probably needs webcal prefix, may not work in all settings. 

There are options to tweak feed: