I've just reposted this (my own post) slightly edited from the battery thread, at John Camp's suggestion, trying to put a better title on it.
The full specs just leaked on 43rumors, and nothing bad, but nothing groundbreaking. The version 43rumors has looks Google translated, so my apologies if I mis-interpreted anything from Google gibberish, especially about external power... I hope that isn't the actual English version of the press release
Here are the power specs...
870 shots on two batteries (CIPA) - almost exactly the same as the E-M1 mk II, which is 440 on 1
2580 shots on two batteries under unspecified low power test conditions (probably similar to how people get 900 shots out of a Z7)
Will run on either 1 or 2 batteries (no mention of whether some fast modes require the second battery, so not clear if it can use them in parallel for higher voltage).
Charges batteries in-camera from either an Olympus AC adapter or USB-C - charges with power off.
Also seems to power the camera from USB-C (apparently without charging).
Here are some other interesting specs:
18 fps, 20 mp (widely publicized)
The specs say it's a sensor "with a new coating", although earlier 43rumors posts have said it's an actual new sensor. If it's the tried and true sensor, PhotonstoPhotos has the E-M1 mkII with nearly two stops less maximum photographic dynamic range than the comparably priced Nikon Z7.
If it's a new sensor, maybe it picks up a stop of DR and becomes competitive with the best of APS-C, while still lagging the best FF cameras?
About the same width and depth as a D850, although significantly taller.
Within a SD card of exactly the weight of a D850.
World's best image stabilization - they claim an extra stop above the already rock-steady E-M1 mk II. The best performance (per Olympus) is on the 12-100 mm lens at 100 mm (they're claiming ~1 second, by my count)
50 MP high-res mode handheld (80 MP on tripod)
Built-in "neutral density filter" with five settings - this appears to be a computational effect, not any sort of reduction in light reaching the sensor.
Has twice as much video bandwidth in Cinema 4K (4096 by 2160) as in regular 4K. Cinema 4K is a GH5 like bitrate.
The EVF is good, but not one of the most modern "super EVFs" - 2.36 million dots (like a Fuji X-T2 or E-M1 mk II), while some modern Sonys, the Nikon Z series and the newest Fujis use 3.7 million.
IPX-1 weather resistance - the first time I've seen any camera company claim an IPX rating. Looking at the IPX-1 specs, the Olympus E-M1 original and mk II, Nikon D850, Z series and D5 (plus predecessors), Fuji X-T2, X-T3 and X-H1, Pentax (most of them) and Canon 1D/1Ds/1Dx series are all close to meeting it... It's basically heavy rain falling vertically for 10 minutes, and none of the above should have any problem.
As far as I can tell, an interesting, but extremely niche camera... Unless they've made huge improvements to dynamic range (and have a perfect stitching algorithm), the 50 MP multi-shot will be far inferior to any number of smaller, lighter 40+ MP cameras with FF or beyond sensors. It's actually larger and heavier than the GFX 50R or the X1D (although the lenses are much smaller than medium format lenses). The Olympus PRO lenses are large and heavy enough that it's going to be bigger and heavier than a Z7 (including lenses) until you reach significant telephoto focal lengths, and even there the Nikon PF lenses will keep it close.
One practical application I can see is mid-range sports photography (willing to accept significant size, weight and cost, but not a 1Dx or a D5). It has fast AF and an extremely high frame rate, and its overall responsiveness should be superb. The problem is the Sony A9 (with all of the above plus a superior sensor 4x the size) at around the same price when on sale. Right now, the A9 is back up to $4500, leaving a bit of room for Olympus, but will Sony drop it back down to $3500 for the next promotion? Once it's been $3500, there's little reason to think it'll stay $4500.
The application where Olympus has everything else beat is anything where image stabilization exceeds all other considerations. If you're shooting video under absurd conditions (while skiing, etc.), the "gimbal included" E-M1x is going to be very interesting.
It'll probably also grab some E-M1 mkII owners, although many will wait for a mkIII that is closer to what they have in size and cost. I'm not going to recommend it to my E-M1 mkII shooting friend unless he really wants the extra stop of stabilization (or there's a sensor breakthrough). If it had come out while his son was still playing college baseball, the speed would have been a perfect feature.