Apparently it has entered the shops only a few days ago.
The latest remark in that thread ("Does seem to have a problem focusing") isn't encouraging. - When I wanted something new after using the SX50 for four years, I seriously considered the Nikon P900. Even today I'd prefer the heavier model P900 (over the B700) which is available used for circa Euro 400.
On the other side, you mention "birds in flight". And that was exactly the reason why I finally bought the Nikon V2 and the 70-300CX lens.
What these superzooms P900 or B700 can offer, at best, are small upgrades over the SX50. Their 5 or 7fps and the slow autofocus still isn't sufficient for much BIF.