You should be looking at multiple communities on the same topic just as a matter of course. Single mega-communities really aught to be discouraged, since they actually crush meaningful engagement (most posts don't ever get seen, most comments don't ever get seen, etc.)

If you follow multiple communities on the same topic, you can get the same kind of constant content stream -- if that's what you're concerned about -- while also actually having your contributions noticed.

Plus, not having single points of failure is the lesson everyone should be taking away from Twitter and Reddit.