I have been developing my own version of ABCDEF+ priorities combined with scheduling to achieve something similar. Thanks to this post, I have actually made changes to the definitions of each priority level, which has clarified things greatly.
If you define the priority levels in terms of Must Do Immediately (A), Must Do (B), Should Do (C or D), Could Do (E or F), and Someday/Paused (P), and then combine that with scheduling, you can get the important things to float to the top by sorting by priority first, then by scheduled or due date. If you hide everything that cannot be done now (usually by hiding everything with a start date after today), you get a good list of what needs to be done now, listed more or less in the order you described.
Separate views for "scheduled items today," and "unscheduled items" are also useful so things don't fall through the cracks. This way you don't have to schedule everything and things still get done.
I appreciate your post. It has helped a lot.
One challenge that I have struggled with are tasks that aren't quite "must do," but are more than "should do." This actually happens a lot when you are creating something new, such as a website or app. You wind up with items that you think should be part of the project, and would be very very beneficial, but aren't actually required.
For example, let's say you are building a project management app. To create a minimal viable product (MVP), there are certain things that you must have. Those are "must do." And you have features that would be nice to have. Those are "should do" or even "could do." But there are certain features that are so beneficial, it'd be a mistake not to do those before the other should do's.
If I label these items as "must do," it dilutes what "must do" actually means. if I include these in "should do," it gets lost in a list of should do's and things are not prioritized correctly.
My current solution to this dilemma is to create a priority level that sits between "must do" and "should do." I am not sure what to actually call it though. I suppose, technically, it is just a higher priority "should do."