In the high end dap market, it is not quite correct that ZX2 is overpriced.
In the level of one grand prices, ZX2 fills a gap with its android-based properties, build, flagship sound quality, streaming, Spotify & tidal use with excellent battery life.
The other two main options who do the job at competing price level are, as told, AK 100 II, and Cowon Plenue.
And as you know, the battery of these two are nowhere near Sony, where Cowon only spares some 5 to 7 hours per charge. Astell & Kern is just a bit better than Cowon in this respect.
Besides, ZX100 is the first device from Sony on its own kind, and so logically it is not a successor of any model. I guess we should try to read this as an attempt from Sony to enlarge its Hi-Res products.
So which gap the ZX100 fills..? I think it is aimed at serious and minimalist listeners (like the writer of these words) who want grand sound, coupled with handy form factor and hassle-free battery life without the android gimmicks.
In other words, it seems to be the response of Sony to the call "Hey Sony, give us a better A10 / A20 with the sound of ZX2 keeping the simple Sony OS".
And yes, despite losing its double ground, I expect ZX100 to be - quite - at the same tier level with ZX2 sound quality.