It already is shaping out. It's called "DevOps."
As a sysadmin with 10+ years of experience moving into development, I agree. The only issue with DevOps is that unless you have a good CS or programming background, you need to spend a few years studying up on coding, coding tools etc. A lot of companies looking for DevOps are asking for Senior Developers etc instead of senior SysAdmin experience. I have however seen one or two companies starting to hire both too balance the knowledge but this might just be experienced managers :)
None had passion for Linux or sysadmin per se. It was just a job they could get with enough pay and lifestyle (stable location, hours etc) they wanted. When they got older, they simply moved onto different jobs that they thought could pay them more or enjoyed more.
I do wonder, how the job market of linux/sysadmin will shape out in 20 years...