Within my niche practice of recruiting attorneys exclusively for companies, 90% of the lawyers my search firm has placed in the past four years came with current or previous in-house experience. Our mix of placement backgrounds was closer to 60/40 just ten years ago, meaning almost half of our placements were lawyers moving into their first in-house position.
I think this is a meaningful observation that speaks to change that has occurred on a boarder scale. Specifically, law firm career paths and in-house career paths are increasingly viewed as two divergent roads. It used to be much easier for a law firm Partner to move in-house as, to stay with the metaphor, the transition was viewed more as just changing lanes.