Before the listCollections command came about, drivers/users could run a count on systems.collections to find how many collections are in a database.

Moving to use dbStats now, but that returns how many collections are in a database, total.
In mmapv1 you have to -2 as there are two system collections.
Using WiredTiger, the number reflects how many user collections there.

This is a request to make the number of user collections available somehow, likely in dbStats.

Getting a count with a filter/query is needed too.