I have a P900, so am familiar with issues associated with that sort of camera. The P900 has very good stabilization btw, the P1000 will likely also.
The two things that make the deal for me are RAW in stills and 4K in video. The P900 does not have RAW files, so you get whatever the camera's white balance decides to give you, and generally I found the colors it produced not right. And the IQ is such that playing around with the file in post degrades things too much. Far too yellow in most cases, especially scenes with a lot of green in them. With RAW you can do the color yourself, a big plus IMO. The second thing is the 4K. The video on the P900 is best termed as "unfortunate", largely due to the terrible compression in the footage. You do not get a high bit rate and the encoder is clearly making a lot of compromises (I would guess due to the limitations of the processor). Later on the B700 was released (the P610 successor) and the video on that was a lot better (still not up to what we see from Sony cameras, but an order of magnitude better than the P900). I expect that the P1000 will be at least as good, and possible somewhat better since the B700 is over a year old now. Supposedly the P1000 has the latest processor and fast AF (likely a similar system as that which will be used in the Nikon MILCs when they are released), so it should be a vast improvement over the P900 in that regard.
You can't expect fantastic performance compared to regular cameras, but keep in mind that this is a highly specialized camera, for use where normal cameras don't have enough reach to be useable. The P900 did the job well, outside of the RAW and video issues, as long as it was used correctly. You need very good light otherwise IQ suffers a lot, and you need to take a fair amount of time to compose the shot (you can't just snap away and expect good results)