The full specs are out for the new Panasonics (well, other than video data rate, and, if that's REALLY high, "videographers" could be the answer to the title question). Like the E-M1x, I'm having trouble seeing who this one appeals to. In some ways, it's similar to Nikon's launch - a capable, but unsurprising 24 MP camera and a pixel monster.
There are two differences from Nikon's launch, though (both of which seem to go against its success). The first is that there is neither a lens roadmap nor a significant existing system (ignoring the ~6 worldwide owners of the Leica SL, for whom these bodies are certainly worthwhile upgrades).
Yes, the L-mount offers first-party adapters for Leica M and R mount lenses, but both of those are easily adapted to any mirrorless camera on the market (and, in the case of R, even some DSLRs). By contrast, Nikon's offerings fit into the whole Nikon system (flashes, batteries and other accessories are shared with Nikon DSLRs), and the trouble-free first-party adapter brings access to many million Nikon F mount lenses, which are much harder to adapt to other mirrorless systems than Leica M and R lenses.
The other difference is that this is not a compact offering. It's the largest and heaviest mirrorless on the market, other than the E-M1x (whose market I also question), and the medium-format Fuji GFX50S (20 grams heavier, with the viewfinder). The other medium-format options are lighter! It's the size and weight of an EOS 5D mkIV.
Of the three initial lenses, the 24-105 is reasonably sized (a little heavier than the equivalent Sony, exactly the same as the Canon DSLR lens, and a tiny bit lighter than the Canon R lens). The 70-200 is heavier than Canon and Nikon equivalent DSLR lenses or the Sony mirrorless lens, and the 50mm f1.4 is the weight of the massive 55mm Otus and substantially heavier than the (already huge) Sigma Art 50mm f1.4! The only remainingquestion is whether that 50 will manage to be heavier than the forthcoming NOCT-Nikkor, which is more than a stop faster (the Panasonic lens is substantially heavier than the f0.95 Noctilux)? Note that Nikon also makes a reasonably sized and priced 50mm for the Z mount...
Unless you own a Leica SL, why would you buy this over Sony? Nikon? Canon? Fuji medium format? If you choose Sony, not only are there are much lighter bodies with very similar features to both Panasonics for hundreds less, there's a full system of lenses and accessories. If you pick Nikon, there are very similar, but much lighter, ergonomically excellent bodies with a small but growing line of excellent, lightweight lenses - and access to the whole F-mount lineup. All other accessories are shared with Nikon DSLRs. Pick Canon if you think the lenses we're seeing point the way to interesting bodies and more interesting lenses, or if you have Canon DSLR lenses... Fuji medium format offers the best image quality now and a clear road to 100 MP, 16-bit image quality later - and the entry price isn't much more than the S1r.
Yes, I chose something else (Nikon Z and Fuji APS-C), and I knew roughly what the Panasonic would be like when I bought the Z7. What puzzles me, though, is that I can't figure out why anyone other than a Leica SL owner would choose Panasonic over other options.
If you prefer Sony to Nikon, that makes rational sense (more native lenses, for one) - I can see it easily even though I chose Nikon. A Canon preference is either a statement of optimism about unfulfilled potential OR an addition of mirrorless to a Canon system - either of which makes sense. Fuji (or Hasselblad) medium format makes sense if ultimate image quality matters more than bulky lenses...
The others all have their niche - and this holds if you include Fuji APS-C and Micro 43. Fuji has the best darned APS-C system out there, with great, relatively compact lenses and a lot of the performance of 24 MP FF. Micro 43 actually fits in three separate places. The smallest Micro 43 bodies and lenses are much smaller than anything with a bigger sensor (although they have significant compromises). The Panasonics offer class-leading video features, and the O-MD line offers performance for sports photographers for far less money and weight than you can get it elsewhere.
Whee does heavy, bulky, expensive Panasonic FF fit?