Hi everyone, as promised, here is an update to let you know this feature is now available to all customers, and we have included an option to set All activity as the default view for all tasks 
You just need to select “All activity” and your choice will persist for future tasks until you change it, if you choose so.
This will hopefully solve your requests on this thread to have all task activity visible always.
Let me know if you have any questions or feedback, I will make sure to pass your suggestions to our product team for consideration in the future!
Have a nice weekend!