Tony Northrup (Youtube) has listed his opinion and the factors:
Many photographers love the Micro Four-thirds mount for its small size and big feature set… But, increasingly, full-frame mirrorless cameras are a similar size and produce undeniably superior results. With Canon and Nikon joining Sony in the full-frame mirrorless market, and Fuji creating value-oriented APS-C cameras, I think it’s inevitable that those lens mounts will lure most new photographers. Additionally, many existing Micro Four-Thirds photographers will be lured to competing camera systems because of the cleaner images, better low-light capabilities, and wider selection of fast lenses. If nothing else, people think full-frame sensors always produce better images, even if that’s not always true.
First, we *currently use* 10 MFT cameras: 8 Black Magic Studio cameras and two GH5s for video. Most of our videos are shot on MFT. In addition, we own a G9, EM-5 II, E-M1 II, E-M10, and Inspire 2 drone with MFT camera. We have more than a dozen of the best MFT lenses, and we frequently adapt non-MFT lenses to the MFT mount because it’s so versatile. We’re HEAVILY invested in the system. We believe in it and built our YouTube channel on it.
I predict Panasonic will gradually move away from MFT. Not overnight, but 5 years from now, I think Panasonic will no longer be releasing MFT equipment. I think they’ll be putting all their energy into their full-frame mount, and I think that’s the right choice.
Factor 1: The compact camera market (“bridge cameras” in 2008-2012) that MFT was designed to address continues to be replaced by smartphones. Nowadays, people aren’t interested in small cameras, because their smartphone is “good enough.” For many, there’s no need for something between a smartphone and FF.
Factor 2: Full-frame sensors will continue to get cheaper. The sensor is a smaller % of the camera’s cost. As evidence, an MFT GH5 and E-M1 II are $1,700, more than the FF 6D, GH5, or D610. I’m not suggesting those cameras match the MFT cameras for features – they don’t – I’m just saying that the cost of the sensor previously was the biggest factor in the cost of the camera, and it no longer is. Panasonic can put the tech we love into an FF camera and it won’t be much bigger or cost much more.
Factor 3: The marketing myth of “smaller sensor, smaller lenses” is largely dead. People understand the value of equivalence in 2018. The Panasonic 10-25 f/1.7 is evidence of this, as is Fuji’s 33mm f/1.0. The number of videographers, including ourselves, that put the Sigma 18-35 f/1.8 + a speedbooster on a GH5 support the idea that we *want* to use Panasonic bodies, but we *need* FF results.
Factor 4: The marketing myth of the “bigger sensors = better results” won’t die, despite my personal efforts at educating buyers. We teach that you can achieve the same results with small sensors if you have the right lenses, and I wish that Fuji and Panasonic would put 100% of their effort into making faster lenses for their existing mounts. Both companies, however, separately decided that they needed to divide their R&D budget and make larger mounts, and we can’t undo that.
Factor 5: The interchangeable lens camera (ILC) market overall is shrinking, meaning R&D budgets will also need to shrink. The mirrorless ILC market is also becoming more competitive because of Canon & Nikon. More people are dividing a smaller pie. Everyone can survive, but they’re each going to have to eat less, and that means making sacrifices. Every dollar Panasonic puts into product development is a dollar they’re not putting into their FF platform, and it *will fail* in the fight against the bigger budgets (and head start) of Canon, Nikon, and especially Sony (the #1 player).
Factor 6: The M43 system was not designed for phase detect autofocus (PDAF). On-sensor PDAF wasn’t around at the inception. As a result of this fundamental missing feature, there are zero M43 cameras that can keep up with Canon, Sony, and Fuji for sports, wildlife, action, and video tracking (and yes, we tested that camera you’re thinking of). They can give future M43 cameras PDAF, but none of the existing M43 lenses have the focusing motors they need to take advantage of it, so no matter what, you’d basically be starting over.
BTW, I know Panasonic’s official statement is that they’re continuing MFT development… but I’m jaded because I’ve been lied to before. Samsung said they were continuing NX development. Sony said they were continuing A-mount, Nikon said they were continuing the 1, Canon with the M… companies ALWAYS say they’re going to continue investing in existing mounts, and they NEVER announce that a mount is dead.