Careers will soon be merged into Stack Overflow.
Only two sites are concerned by this change, because there’s currently only two kind of jobs on Careers: developers and system administrators.
Because careers.stackoverflow.com isn't careers.stackexchange.com (and uses some of the Stack Overflow design) most jobs advertised on Careers (which will become Stack Overflow) target developers.
Of course this issue predates the current change but it will enhance targeting for developers at the expense of sysadmins, thus making things far worse because there would be no longer separate site with a separate design and separate accounts (so targeting fewer people).
Going to Stack Overflow for finding non developers Jobs would be like the situation of this famous sketch.
Result of the change:
I understand you will keep encouraging posting sysadmin jobs on Stack Overflow instead of Careers. But such change will definitely put a strong STOP to the idea of advertising non developers jobs for employers.
This also means Server Fault users would need to create a Stack Overflow account even if they do nothing related to questions/answers on Stack Overflow. Those who have a Careers profile, but not a Stack Overflow account will also probably get a Stack Overflow account.
So please don’t move what remains of this feature !
The real integration path you’re describing would have been to create new jobs sites first (at least for Server Fault) and only move Careers to Stack Overflow after.