Thanks for your experience and the value you find in IS handheld, over using a tripod.
I think for an African Safari, dedicated to photographers, the land rover is setup for Arca Swiss type mounts to be attached, (see
http://reallyrightstuff.com) and the most ambitious long lenses.
For the dense jungle canopies in South America, at least in my limited experience, (and I am no expert wildlife photographer), balancing an excellent, even sturdy tripod on a moving boat is quite risky. More than a few times I was in danger of losing the tripod and rentead camera as the boat suddenly swerved to avoid a low lying rock or crocodile!
I could have easily brought sandbags to stabilize the tripod and heavy lens, (or paid the fellow sufficient to allow me to screw a bracket into the deck), LOL!
So the by far lighter MFT system with a 100-400 lens band great IS becomes competitive.
Real experts would indeed have the tripod fixed to the boat but also have not just a side-mounted gimbal, (to swing and track the heavy telephoto lens at will), but also Better Beamer fitting to strobes, to project the light needed to illuminate Deep into the canopy.
All I know is that, honestly, I didn’t have the skill and setup, last time around to handle my big lens tripod setup because of limitations in movement and inherent instability. I know enough now to overcome these shortcomings but feel that a lot more tryouts of competing setups is advisable before that expensive wildlife trip!
Asher