SG: doc channel limit or performance impact of adding channels

First comment:

Is there a hard limit on the number of channels that can be created in Sync Gateway? A customer expects to create more than 1 million.
If there are no hard limits are there any expected performance hits? For example a background process that runs through the list of channels to do some work, would a large number of channels potentially create an issue?
Is there a limit to the number of channels a user can subscribe to?
Would a large number of channel subscription possibly cause some type of performance issues for that specific user, during syncs etc?

For example:
solution A.
There are 1 million documents, distributed across 200 channels, with 10k users subscribed to the various channels.
solution B.
There is 1 million documents, distributed across 1 million channels (each doc in its own channel), and 10K users subscribed to those various channels.
Would solution B introduce a significant more amount of overhead/performance issues then solution A?

CBSE-3433

see other comments: https://github.com/couchbaselabs/couchbase-mobile-portal/issues/573