Q: When will SMB 3.0 be available for Windows 7?
A: SMB 3.0 is part of Windows 8 and Windows Server 2012 and offers improved performance, and most importantly, new features around transparent failover and active-active sharing from file server clusters for specific types of server workload such as SQL Server databases and Hyper-V virtual machines.
At this time the active-active file sharing that allows multiple servers in a cluster to offer the same file share concurrently is only supported for enterprise scale-out applications like the ones I mentioned and not for general file sharing such as for Word and Powerpoint documents.
Therefore adding SMB 3.0 to Windows 7 wouldn't bring a huge amount of value since enterprise applications do not run on client OSs. SMB 3.0 is a feature of Windows 8 and Windows Server 2012.
SMB 3.0 does bring value to Windows 8 clients. In addition the performance gains, the new SMB multichannel capabilities make the transition from wired to wireless and vice versa a smooth process and avoids breaks in file copy operations. SMB encryption offers encryption without IPSec so don't think there is no value with SMB 3.0 for Windows 8.
If you have Windows 7 clients talking to Windows Server 2012, they will negotiate to the lowest common protocol which would be SMB 2.1 enabling communication, while not taking advantage of the SMB 3.0 specific capabilities.