I’ve begun using Strides to record my BP and have resorted to entering it as 128.76 to get both parts of the BP reading. Allowing 2 data items would not only solve the BP issue, but several others: time and heart rate for a run or bike workout, time and pace for biking, weight and %fat, and I’m guessing many others. As a product manager myself, I understand why you want to keep trackers generic and multipurpose and why you rejected a specific BP tracker in the past: this idea satisfies both goals.
There may be other ways to satisfy this user requirement such as tracking each data item separately but allowing them to be reported together.