The first (less convincing) sign is that Apollo Justice's (loud) Nintendo Europe webpage has the string "AceAttorney3" in its URL. That doesn't really mean that the third Ace Attorney game isn't happening, rather that Apollo Justice is the third Ace Attorney game to be released, and that whoever created the URL didn't save a space for the real AA3.
More troubling is the fact that there is a site for Trials and Tribulations, but there are no longer any links to it. Could this point to a cancellation? Court Records members speculate that T&T would get a higher PEGI content rating than the other Ace Attorney games, and because of that, Capcom wouldn't benefit from releasing it. In any case, both the U.S. and Japan have cheap and plentiful Trials and Tribulationses. Feel free to partake!