Worms, by Team 17, with unlimited character changes. It's still turn based, but it does not change much for the purpose of this discussion.
Are there any multiple characters platformer that sounds like this ?
To be honest, I think allowing unlimited, instant character switch would result in consistent ease of the puzzle elements. I guess that would be what you're looking for!
Commandos, by Pyro studios does not have explicit planning phases but the phases naturally emerge. The game is mostly slow-paced, sequences requiring careful timing and fast-paced actions (as far as I remember) can be easily interrupted as most levels offer plenty of safe zones.
Not that I know of, but your idea seems interesting and commandos is a great game to get inspiration from
It's also worth noticing most levels I recall started from a safe state. This effectively allowed an initial "plan" sequence which is ideally as above described, albeit implicit.
It allows unlimited character switch and still retains a strong strategic/tactical element. Completing even the simplest missions could easily take 10+ minutes.
I'm afraid you might be misunderstanding the meaning of the terms I'm using in my previous post.