Spring 2016: Nintendo HH
Holiday 2016: Nintendo console

Holiday 2019: Sony & Microsoft console

2017 with Nintendo's new console.

If there is another Gen for MS it will be interesting with Phil Spencer at the Helm. I think things will go a lot better with Spencer as head of everything Xbox. If he gets a shot to head up a new system.

Hm... gonna say 2018 for Nintendo and 2019 for Microsoft and Sony.

2018 with the HDS. Backwards compatible with the 3DS (and hopefully the DS?), a bit more powerfull than the Vita.
2019 with the new Xbox and Nintendo consoles.
Sony will use their advantage with the PS4 to wait a year and create a system way more powerfull than the other two in 2020, and come out with a lot of games already and not like the PS3 (and kind of PS4 too) first year drought. This time diference won't affect PS the same way the 360 did to the PS3.
Vita won't receive a proper successor. It will be a Bravia Mobile with gaming capabilities.

And somewhere between the 9th and 10th gen, the Videogame bubble will explode and we'll have another videogame crisis.

New nintendo console will be announced in 2016 and launch late 2016 or early 2017. The xbox will be 2017 or 2018. The ps5 will be 2018.

If Nintendo's sales pick up next year when all their big games come out, I think 2018. If not, 2017.

Early 2017 to Summer 2018, though I'd say Q4 2017 to be safe. That's when I expect the next Nintendo handheld to come out. And by around the same time, we'll know something about Nintendo's next console too.

Damn! You beat me to it. Only I was going to say Nintendo and stuff...

2017 - Next Nintendo handheld
2018 - New Nintendo and Xbox Home console
2019 - New Playstation Home Console

For 9th gen I'm expecting there to not be a Playstation Handheld