The reason I ask - most of what you hear out there are stories of people being "freelancers" where the work is somewhat of a commodity (wordpress, webapps, etc) and they have to differentiate themselves by quality of work/communication. But it sounds like you are more on the specialized/niche side, with retainers and being a "consultant".

So far I've been tackling the "builder vs manager" problem with: joining small startups or starting my own. The good news is that the last 2 startups I've joined have hit rapid growth, but the (bad) news it that I keep getting pulled into management. I know that I can/should hold a stronger line and say "No, I want to be an IC", but it's hard when my boss pushes back that it'd be better for the company if I manage. None of this is complaining/whining per-se, but your solution is potentially a win-win where I can avoid the mis-aligned incentives (ie: holding the line on IC vs management).

As far as engagement length, my longest engagement is currently 6 months. Generally I don't have an issue with getting promoted into management as an independent contractor, as my loyalty is ultimately understood to be to my own company, and I make it very clear that I do not wish to become a manager. If those terms aren't acceptable, hey, I'm a contractor, everyone's welcome to terminate the relationship with zero hard feelings whatsoever, which is both an advantage in the current economic environment as well as the reason I need to maintain a pipeline of opportunities no matter how well things are going.

It's the weirdest thing to me this is how it can be but it's so real.