I poked around a little bit but didn't see this, so forgive me if this has come up elsewhere.
I had another task/project management app that had a feature that allowed me to check a box within the project to "complete subtasks in order" so that only the next task would be displayed and the following task would not appear until the current task had been completed.
For example, you create Project A, then enter tasks Step 1, Step 2, Step 3. You select the option to "complete subtasks in order" for this project. Now, in the Focus List (assuming you have subtasks enabled for the Focus List) only Step 1 is displayed. Step 2 will not display until Step 1 is completed.
Honestly, this was one of my favorite features of that app. There are two primary advantages: 1) It is true to GTD methodology for truly focusing only on your next action (not viewing your whole list of tasks; that's what the GTD 'next action' idea is really about) and 2) it significantly reduces screen clutter. I would love to look at only my next actions and nothing more. Plus you're not locked into anything: you can always jump into the project if you need to complete other tasks that are elsewhere on the list. This would just be something in keeping with the idea of a Focus List.
I think a lot of people would like this feature if they had it. I know I found it indispensable on my other app. I'd love to see it with Todo. As it is, if it's not possible (or popular), I do find it workable currently to disable subtasks in the Focus List and simply tap the project for the next task. But having used this feature already elsewhere, I gotta say it's pretty nice.