I have a requirement to create stream (new and based on existing stream's baseline) and project using the SCM command line but I dont see any command or subcommand which can help me to do that.

Any idea?

The ability to create a stream can be tracked in the following work item:
"169093: Add scm CLI option for stream (create stream / delete stream / update stream)" (https://jazz.net/jazz/resource/itemName/com.ibm.team.workitem.WorkItem/169093). Feel free add comments there expressing your interest.

Unfortunately, I am unaware of a way to programmatically create a project area. The ability to create a project area or team area is outside of the realm of SCM. I.e. You could imagine a build of RTC in which SCM was stripped out leaving only "Work Items Tracking" features.... Project areas and team areas would still exist. This is why the ability to create a project/team area using the scm.exe does not exist (and probably will not exist in the future).