Behaviour Triggers inside Sequences

It would be great to be able to create a task in sequences depending on email behaviour.


For example, the first step in a sequence is to send "Email 1", i'd like a task to call that customer to be created ONLY if they've opened the email OR Opened but haven't made a purchase in X hours/Days.


I know this is doable via Workflows, but it would be much handier to be done via sequences.