14 DAY TRIAL // During the past six months, NVIDIA has had to cope with a sudden cancellation (or near-cancellation) of TSMC's 20nm technology and the subsequent need to rebuild the Maxwell architecture from the ground up for compatibility with 28nm.
Because of this, the high-end Maxwell-based graphics cards aren't likely to debut before the late third or fourth quarters of 2014. Or, in layman terms, before late September or the October-December period.
Nevertheless, there is at least one party on the world wide web (VideoCardz) that believes NVIDIA will reveal the GeForce GTX 880, and maybe the GTX 870, at Gamescom, the gaming expo held each year in August in Cologne, Germany. That would mean that we only have three or four weeks left to wait.
The GM204 will power the GeForce GTX 880, and the GTX 870 for that matter. However, it is quite probable that NVIDIA will restrict itself to a simple teaser video, and maybe a partial specifications release.
Then again, the GeForce GTX 750 and 750 Ti came out quite early this year, and they are, too, Maxwell-based. So, presumably, NVIDIA already got the hang of implementing Maxwell on 28nm technology, so it should be able to do it easily enough for the high-end cards as well. We can only wait and see.