My required feature list
Todoist really is a beautiful application, and I do find much to like about it - that's why I've paid for it, and have put enough of my world into it to truly exercise it. However, it isn't quite to what I would consider a viable task management system for anyone serious about such things yet.
The six things I really need from Todoist for it to remain my task management system of choice (in no particular order):
1) Start dates: this is probably the biggest deal killer for me. A number of tasks in my world occur as intermittent actions through a period of days, but are not readily broken up into smaller tasks (plus there's a point at which granularity is counterproductive - task management takes longer than the tasks you're managing). Additionally, the bonus is that it would assist with time management - I could look for tasks with an expected duration of two hours if I find myself with a free block of time, for example.
2) Project properties: Projects should have optionally inheritable elements such as start date, end date, labels, notes. This allows for quicker entry of sub-projects and tasks, as well as offer a means of a central location for project information (notes, intended full schedule, etc).
3) Ability to filter within a project - I should be able to build a filter that says I want to know what the overdue tasks are in a specific project, for example.
4) Recurring tasks end dates: this is also a big deal for me, as I do have many tasks which recur for a period of time, then end. It's not a valid long-term solution to say to archive the task when you're done with it - that requires me to once again keep schedules in my head to remember when it ends, rather than in its proper place in the tool. That might be okay if I only have a couple of such tasks, but when I fully move in, *many* of my home and work projects include multiple limited length recurring tasks.
5) Export/Import via CSV files: This would enable me to better report on my work (by exporting my data on specific projects, ideally!), or add projects and tasks as a bulk action, doing the heavy lifting of repetitious information in a spreadsheet, rather than typing things in one by one.
6) Better context information on items in a filtered view, specifically by making parent task information available without having to leave the view - as an example, it would be good to be able to mouse over or right click and see a hierarchical path for a sub-task, showing project, sub-project, parent task information as appropriate.
With these 6 items, Todoist would become a viable "keeper" for me. Right now, without these items or any transparency into what's coming up soon or truly in the pipeline, I cannot trust that this application will sufficiently serve my needs over the long run, and I haven't been willing to fully commit to moving everything into it.