I saw this point on Technet article about RBS.
The local FILESTREAM provider is supported only when it is used on local hard disk drives or an attached Internet Small Computer System Interface (iSCSI) device. You cannot use the local RBS FILESTREAM provider on remote storage devices such as network attached storage (NAS).
Does it mean we cannot use FILESTREAM in case of SQL Failover Cluster because Failover Cluster only works on NAS? But the thing is NAS is made available locally when setting Failover Cluster so may be FILESTREAM will work but I am not sure about it.