When trying to clone a PDB from another PDB within the same CDB or from another PDB in a remote CDB (using DB Link), it requires putting the source PDB in OPEN READ-ONLY mode.
I would greatly appreciate if you could consider adding an option to clone PDB when the source PDB is in OPEN READ-WRITE state. This will eliminate the downtime that is required today for PDB cloning operations.
Update: PDB hot cloning is now possible with Oracle Database 12c R2:
The source is the existing PDB or non-CDB that is copied. The target PDB is the clone of the source. The source can be a PDB in the local CDB, a PDB in a remote CDB, or a non-CDB. The CREATE PLUGGABLE DATABASE statement copies the files associated with the source to a new location and associates the files with the target PDB. When the CDB is in ARCHIVELOG mode and local undo mode, the source PDB can be opened in read/write mode and fully functional during the operation. Therefore, hot PDB cloning is supported.
For more information refer to: Database Administrator's Guide