Everything I’m not working on is either on hold or deferred, so I guess my “available tasks list” is kind of like Things’ Today list?
That’s exactly how I work, as well.
For me, one of the philosophical quirks of Things is that it enforces a temporal perspective. The flow is geared towards moving tasks to Today. However, for me, something that needs to be done Today simply has a due date of today. If not, I can do it any other time. And it does not need to be done today.
Instead of Today, I always work from a list of available tasks and I might flag tasks I am working on right now. Perhaps today, perhaps today, tomorrow, and the day after. But is not bound by the horizon of a strict Today.
The defer dates, too, I feel are more suited to my workflow in OmniFocus. Things wants to remind you, explicitly, as soon as something moves to Today. But again: does that need to be completed on that very same day? For me, a start date marks a date I can begin working on a task. And it could happen that a start date and due date are the very same day. And then, accordingly, I will get notified that something is Due.
As far as alerts are concerned, I would love for those to be more flexible in OmniFocus, too. Specifically if a Due app system could be integrated, I could easily abandon Due in favour of OmniFocus.