I can not see where Christians would ever find perfect community until our perception of such is adjusted to accept the fact that our fallen human nature is an inevitable part of it. Jesus' entire ministry was with the lost sheep.
Even if the purest of saints were to isolate themselves from the world, they couldn't escape their own human nature. We do what we don't want to do, and don't do what we should.
Fellowship belongs to those who walk in the light as He is in the light. We love one another as God, through His Son, loved us. Love is sacrificial, and like Jesus, we lay down our lives for one another. I believe this is the essence of fellowship. Not that we find sinless saints, but that we find saints willing to confess their sins to one another because it is only by the Spirit that one confesses with their mouth.
If we see someone in the body of Christ sinning, we are to call them to account. If they repent, we have brought them back into fellowship. If they deny us, then the love of God is not in them and we have no fellowship with them.
The greatest burden to fellowship is the mingling of the church and the world, perpetuated by leaders who refuse to sanctify the communities of those who "go to church".
Beyond that, the fellowship of believers are simply those who are led by the Spirit first. The working out of community develops through the same patience that our Father has afforded us.