Actually, it's been going downhill since the WiiWare exclusive titles in Japan. Apparently it's even WORSE than GTI, as at least GTI got released outside of Japan!Pokemon Mystery Dungeon, definitely.
In my opinion, PMD always had better stories than the main series, so I don't thiink the developers would want to give up on something like that.
I know that PMD has been going downhill since Gates to Infinity, but I really hope there's going to be one for Gen 6 before they announce Gen 7.
If they were developing it at all, I just want to imagine that things got slowed because of adding the Mega Evolution mechanics....
I think the next game will be that Detective Pikachu Game for Wii U, that got announced ages ago. As for handheld, it could be anything from another generic art game, to an App, to another freemium game. If they stick to the freemium route, I hope it will work like Rumble World, as I'd rather pay for a game which has a spending limit, to one like Shuffle, which lets you spend thousands on. :/
Though, what I really want is a proper game, not only worth the retail price, but also not too much for casual/phone gamers.
I honestly think there's going to be a big game crash if people continue with the freemium stuff, as everyone seems to make them and they can be for any device. It just saturates the market or makes games which used to be fun, incredibly limiting due to lack of time/money.