A specific subscription can be suspended or deleted.
New subscriptions can be added no problem but for every new subscription we need to have a new stream subscriber object. A pool of them. Maintaining the consistency between the subscription resources and the subscribers should be coordinated through data process management.

i.e.
```
add_subscription(data_process, stream)
  for each data process in some pool:
    tell process to add subscriber
    create subscritption and activate
```