No frontend access. This means you require all users to log into to joomla's backup. Not good idea
Whats the point in having the calendar if your tasks are not tied to it? Who wants to create tasks then turn around and post events for those tasks?
You're right with the calendar..pretty useless at the moment :D
Hydra is a huge thing and I can impossibiliy work on everything at a time.
On the roadmap you see that I've promised the task/calendar integration in 0.6.5.
It's not there I know but I'm working on it.