I tend to think that obsessions with "one camera, one lens," where not driven by necessity, tends to be a sign of what Tom Wolfe would have called "sclerosis."
Personally, I find that 90% of my pictures are taken with one camera and one of three lenses. But sometimes you need to pull a reverse Maslow: a new type of equipment sometimes makes you rethink old problems in new and more creative ways.
The other thing that people don't want to talk about is that your skills may hit a plateau, and once you're there, the artificial discipline of limiting what you use isn't helping you "concentrate on technique" any more. It's just limiting what you will do with your now-developed skill set.