I use Wunderlist and I know the ability to share tasks is coming to To-Do but the one drawback with Wunderlist was not being able to assign a task to more than one person.

Outlook tasks have 3 priority levels and this app only has two.

There are often similar Tasks or Workflows in business. So it would be nice to have an option to define Templates for tasks/Workflows (Task with sub-tasks and dynamic reminders like 2-weeks after start). This would allow the user to manage internal processes with the todo-list. Maybe it's also possible to start a workflow by sending a mail to the todo-list and giving some attributes in the subject to initiate the details of the task/workflow.

Get notifications for incoming tasks and ability to mark them as completed from the notification.

can change task font and size

Let's configure ringtones individualy for lists

Import specific music
Configure the volume etc

Please allow separate sorting of the completed list - completed should be able to display by date completed

Persistent Notifications/Reminder option!

It would be really useful to have an option that when a reminder is displayed, it keeps showing on the home screen until it's actioned or snoozed, like you can in iOS native reminders. This makes it much better as you are constantly reminded until you manually mark the reminder as complete. This would be so helpful and I've been waiting for this in Wunderlist for years. Please implement this if you can!

Add the ability to tag tasks with priorities important/not important & urgent/not urgent (cf https://en.wikipedia.org/wiki/Timemanagement#TheEisenhower_Method)
Add a cross lists view displaying the tasks in the 2x2 matrix

Please add a “today” smart list of things due today plus a weekly view

Or let Wunderlist continue

Completed items to be excluded from searches and ability to view and search just completed items

I have multiple work accounts and a personal account. It would be good to have all these actions in a single To Do app - with the ability to see them ordered by account, with additional items added being integrated to the appropriate source account.
Is this likely anytime soon?

Choose a list on your watch, and check off items as you go on your watch!

Provide option to share a Group created with other users. Currently have to share per list in a Group Manually and have to track if missed to share any list in a group with others.
I would be fantastic to have sharing options like Parent/Child settings. Like Child List inherent sharing options from Group Parent or can have unique permissions.

It would be great if we could add our own custom priority list to be used for a list.

Default Due Dates and Reminders for new tasks

Allow your completed ToDos to be kept, logged, and searchable. This would allow people to have a searchable log of the tasks and it's notes they've completed if needed. This data can be linked into a user's OneDrive account and accessible with other Microsoft office tools.

The new Steps feature has been introduced to meet the need for subtasks within a task. It is possible to easily reorder the steps and to delete them individually, but it would be highly desirable if the user could Hide/Unhide the list of Steps within a given task. That would decrease task clutter and increase usability. Hopefully, this is on your roadmap for the Step feature...