Hey all - sorry to be late to the party.
I believe that the DD not running on the SysTask table was introduced by prep work being done in order to change the way Reports and Tasks run. We need to investigate further but likely the capability will be restored.
I have to admit that I intensely dislike DDs on SysTask. Prior to the ability to schedule Functions, DDs on SysTask were (and still are) often used to “do stuff” on the regular heartbeat of the Task Agent. A fair amount of the SysTask DD BPMs do not consider how frequently execution occurs and performance complaints, SQL Locking errors, and AppServer Memory issues often result.