best approach of pushing Docs to Millions of users using Sync gateway.

[Faheem]

I am trying to  evaluate  couchbase  Mobile , couchbase lite along with couchbase sync gate is a good  for implementing  use cases where 

documents needs  to  be pushed  to  100s of  thousands  and pleb, potentially Millions of  users.   The pushing of Docs can be  more frequent as well , I have  listed  following two use cases, please  suggest which use case is more  suitable and better performant 

1. We have channels and  users are subscribed to those channels, we might have 100s or  potential can be 1000s or channels and each channel can have Millions of users subscribed to each channel.  So one doc need to be associated to  max 100s or thousands of the channels. So in this  approach we might have to subscribe and un-susbcribe users frequently, which I have read is an expensive operations. Also we would like to know that is there any limit on number of users a channel can have , and what are the performance impact on having more user subscribe to one channels. 

2. In this second approach we would have one channel for each users, so we would have Millions for channel, and then one channel would  have only one user subscribed to it.  But then One doc need to be associated to Millions of channel to push that doc to all of the users. What is the limit  on  number of channels a doc can belong to,  and what is the performance impact if we go with this approach. 

Also like to know what are the user which Sync gateway docs refer to are those app maintained users or those are couchbase users please explain on it a bit. 

thanks

Faheem