A distinction must be made between Vega the architecture and Vega 10.
About Vega 10 we know a few details. The Instinct MI25 uses it and AMD claimed almost 25TFLOP FP16 so the assumptions are that it is 4096 cores at 1500+MHz. After a quick look at the pictures available, the die size appears to be at about 500mm2 but unclear if on 16FF or 14nm. If so, they might be taking a step back in perf density(in FLOPS) but gaining a lot in efficiency and likely utilization in gaming. In gaming it could be anywhere from 10% bellow Titan X(1200$) to beating it by 15% or more. TDP was stated at bellow 300W,remains to be seen how much bellow that.
Vega the architecture is bound to reach GPUs in all price bands and APUs.The APU bit is interesting, if Vega turns out to be a rather large step forward. It could enable certain key design wins by offering what Intel can't and maybe your next notebook would be AMD based - just exploring the possibilities Vega could offer, not aimed at starting any rumors.
@realjjj Alex of JPR was clear that his performance esitmates were educated guesses given AMD has not revealed many key details such as frequency, power consumption, die size, etc. That all comes with benchmarks at the product roll out I suppose.