Milestones are nice, so are checklists, tasks, etc... But to give the timeline some real utility, I'd like to see an object type 'event' added so that we can bring in single events or repeating events and have these reflected in the calendar / timeline. I know that we could bend a task around this, but they are markedly different in my opinion.

Absolutely! We would love to see an 'event' object as well, we are using milestones for these now, it's not perfect at all and messy. +1