I hope not. I have worked quite a bit on Python/Django but I am considering diving into C++ due my recent exposure of the wonderful world of graphics programming (not game development but simulation and visualization).
Nobody is going to penalize you for being the Django guy who can also hack complex C++ and knows his way around OpenGL/DirectX. Far from it, you'll look like a guy with a truly broad skill-set who can handle damn near anything.
The guys who are having trouble are the guys who decided that the knowledge they needed for their 9-5 C job was "good enough" so they stopped learning. That's what kills careers.
Stopping learning is an issue, but employment reality is more complicated. In much of the country the guy who can hack both Django, C++ and OpenGL is unemployable, and the guy who turned his brain off after getting his MCSE can easily find a job.
For instance, this is a pretty typical snapshot of who's hiring in my part of the country:
Individual locales can have particular niche demands or simply end up as technical backwaters where employability depends entirely on your familiarity with, say VB 6.
That's mostly, I think, an argument for moving out of technical backwaters if you're in a technical career. If you let yourself be limited to skills that are more valuable in Minneapolis than the major tech hubs, you're eventually going to be stuck with skills that aren't even valuable in Minneapolis, as the "hot" tech hub technologies become mainstream and finally migrate there way out to the backwaters.
The guys who are having trouble are the guys who decided that the knowledge they needed for their 9-5 C job was "good enough" so they stopped learning. That's what kills careers.