watchapps yes, but insertTimelinePin is already blobdb operation - i.e. insert into the watch from the phone. But phone-side handler is missing. Even JSKit will just provide a feed of pins, while they should still be handled in the phone (rockpoold).
pebble SDK can do pin insertion (emulate jskit pin being delivered over the net) but it merely delivers json object to the phone (via devconnection).
Now - that json should be parsed, cooked, transformed into TimelineItem(TimelineAttributes,TimelineActions) based on local timeline state (new event/update/delete) and resulting blob pushed to the blobdb. So this is the part i'm talking about.
Again, reference implementation is done by Kath here https://github.com/pebble/pypkjs/tre...ypkjs/timeline

Edit: To make it more clear need to clarify terms: Pin - JSON object as described here; TimelineItem - Binary object which could be serialized and pushed to watch; InsertTimelinePin is that wrapper I was speaking about - lightweight attempt to glue events/notifications to the Time Pebbles by creating TimelineItem on the fly from some input params.