FourThirds and moving whole-sale over to MicroFourThirds. And it has gotten louder over time to the point that nearly everybody, from rumor sites to fora, keep repeating this claim incessantly. Why is everybody making such wildly adamant claims?
First, there's the current state of the market for 4/3rds cameras vs µ4/3rds cameras. Panasonic, Olympus' initial 4/3rds partner, has introduced a slew of µ4/3rds models since the standard's initial announcement in 2008. Olympus itself has introduced its third µ4/3rds model, the E-PL1. By all accounts both Olympus and Panasonic can't make them fast enough. Micro 4/3rds is so popular in the Japanese market that according to the latest statistics out of that market mirrorless interchangeable lens cameras (which includes Olympus, Panasonic, Samsung, and Sony) now account for 30% of new camera sales. That's a pretty remarkable statistic for a camera category that didn't exist just two years ago. Then there's the fact that Panasonic hasn't introduce a regular 4/3rds model since the Lumix DMC-L10 in August 2007. Olympus is the only manufacturer of regular 4/3rd cameras in the market, and they haven't announced nor introduced any new models since the E-620 in June 2009, a full year ago. Olympus has been silent about new 4/3rd offerings ever since, instead concentrating on release µ4/3rd bodies and lenses.
Secondly, there's Olympus' own history playing against it. Olympus made the major misstep of dropping the Olympus OM series of film cameras. First introduced in 1973 with the OM-1, Olympus released four professional variants and a matching and expansive lens collection that came to an end in 1987 with the release of the OM-101. What killed the OM series was autofocus. Olympus had built the perfect small mechanical SLR with matching lenses by stripping out everything that wasn't absolutely needed. This left a system that was marvelously small and tight, while in the process painting Olympus into a technological corner. There was no room in either the body or the lenses to provide autofocus capabilities. The best that Olympus could provide was focus assist, which made its first appearance in the OM-30, and required a specially built zoom lens to fully function. Olympus would continue to support the OM-3 and OM-4 up through the early 2000s, but they never introduced another "exchangeable lens" camera after 1987. Instead Olympus concentrated on smaller integrated cameras, both film and digital, for the next 15 years. Olympus wouldn't introduce another interchangeable lens camera until 2003 with the digital 4/3rds E-1.
Canon faced the same challenge that Olympus did, and took a different route. Up until 1987 Canon used a breach-lock mount for its bodies and lenses. First introduced in 1971 with the F1, the FD mount was the Canon mount until 1987 (the same year Olympus introduced its last interchangeable lens film camera) with the EF (or Electro Focus) lens mount. Canon was the first major manufacturer to introduce an autofocus system in which the focus motor was in the lens itself. The other major manufacturer, Nikon, seeing what had ensued with Canon, made the decision not to radically change its mount, but instead adopted an inferior mechanical linkage for autofocus in its first autofocus cameras by placing the focus motor in the body and sticking the linkage out through the bayonet mount (and I know this because I purchased the N90 with the Nikkor AF 35-70 zoom lens, a purchase I would come to regret). While the Nikon decision allowed any F-mount lens to be used on the body, the early Nikon autofocus cameras left an awful lot to be desired.
Canon took considerable heat for changing mounts, but Canon eventually overcame that obstacle and went on to cement its position as a powerhouse in the SLR, and then DSLR markets. What is significant in Canon's case is that Canon had overlapping camera lines that used both mounts. Thus, when the last breach-lock mount camera (the T-90) came to an end in 1990, Canon had the EOS camera line with the EF mount ready and able to carry the Canon standard forward. The two lines overlapped one another for three years, allowing a reasonable crossover from old to new. Nikon eventually overcame its first attempt at autofocus and it has also prospered. But Olympus...
Olympus introduced a series of integrated cameras, first in film and later in digital form, producing highly praised cameras such as the Camedia C8080 and the E-10 and E-20 all-in-one cameras. But Olympus' abandonment of the OM series of cameras left a lingering and very sour taste in a lot of photographer's mouths, pro and amateur alike. That's one of the reasons Olympus was looked upon with suspicion in certain quarters with the initial release of 4/3rds, and it's the reason for the rampant rumors about 4/3rds demise. The rumormongers see current conditions and Olympus' own history playing against 4/3rds.
It all sounds wonderfully grim, and Olympus' critics are rubbing their hands with sadistic glee over what they see as another major Olympus failure in the making. The only problem with this delightfully grim prediction is that it's wrong. Olympus knows it can't just drop regular 4/3rds. They are painfully aware of the repercussions of another mount abandonment. If Olympus were to abandon 4/3rds then they might as well pull out of the entire camera market, because the repercussions of a second major mount abandonment would fatally taint every other camera product they would try to sell going forward.
Instead, I strongly believe that Olympus will merge the 4/3rds and µ4/3rds lines into a single series of cameras based on µ4/3rds. Why? Consider Canon, Nikon, and Sony. They have two interchangeable lens camera categories, one based on APS-C sized sensors, and a higher (and more expensive) category based on 35mm film sized sensors. But they all have the same respective mount between the two categories. Olympus (and only Olympus) has the opposite; two different mounts sharing the exact same sensor. It takes a lot more effort (i.e. time, money, and marketing) to support two different mounts (regardless of how backward compatible the newer one may be with the older) with different lenses than two different sensors using the same mount and lenses.
Olympus and Panasonic have already started down the path of convergence with the initial 4/3rds-to-µ4/3rds adapters that allow older 4/3rds lenses to operate on newer µ4/3rds bodies. I have two such adapters (the MMF-1 and MMF-2) that allow me to use my 12-60mm, 50-200mm, 9-18mm, 50mm, 40-150mm Mk II, and Sigma 30mm regular 4/3rds lenses on my E-P2. These lenses are slower to autofocus on the E-P2 than M.Zuiko lenses, but they do autofocus, and they make stunningly good images. Olympus is fully aware that it needs to enhance contrast detect autofocus (CDAF) performance, and there is at least one patent extant that shows a 4/3rds-to-µ4/3rds adapter with a built-in mirror and phase detect autofocus (PDAF) sensors in the adapter to provide the same autofocus speed as if mounted on an older regular 4/3rds camera.
I believe that Olympus is working hard to merge its two interchangeable lens lines into one, based exclusively around µ4/3rds. They will provide a seamless transition with existing 4/3rds-mount lenses. It's going to take time (I estimate 24 months), but we will see the road-map for this transition starting with Photokina this fall.