This is less a thought about game design, and more a thought about designers themselves.
Looking at my own and others' experiences, game designers seem to learn the most about their trade when they step outside of their zones of comfort.
For example, if designers work on nothing but a single system for years, their design skills - even in regards to their most familiar system - improve if they work on another system in the game. On a broader scale, I'd even say that console design can inform PC game design, and vice versa.
When designers leave their most familiar contexts, while it may be uncomfortable, I think it grants them more opportunities for lateral thought, and greater game-making potential.