JourneyMap 1.16.5-5.7.1 adds "/waypoint" command to create a new waypoint.
I think it's OK to add a waypoint even JM don't have a API now.

The API classes still exist so it will probably be fixed in a future JourneyMap version.

Regardless of whether they re-implement the API or not, simulating command calls is too hacky of a workaround for me, I'd rather have no support at all if it came to that.