The last time platformers were big was in the PS2/GameCube/Xbox era. Jak and Daxter, Sly Cooper, Ratchet and Clank, Mario Sunshine, Ty the Tasmanian Tiger, Rayman 3, Crash Bandicoot, Tak, Dr. Muto, Voodoo Vince, Blinx, and Psychonauts. The last "big year" for platformers was 2004 with Jak 3, Sly 2, Ratchet and Clank (2?), Ty 3, Crash Bandicoot, etc. etc. were released.
However in the next generation there were hardly any platformers, especially 3D platformers. There were Ratchet and Clank, Mario Galaxy, a couple OK Sonic games, Epic Mickey and.... that was pretty much it.
The genre that became popular during this time was of course the first person shooter. Because people "moved on" from the platformer genre which is deemed "kiddy" they were no longer viable to develop. For example, Banjo Kazooie: Nuts and Bolts was originally planned as a true 3D platformer but because they feared it wouldn't sell it was redone as a sort of racing game.
2D platformers have made a HUGE comeback in the past few years, so it makes sense for 3D platformers to follow suit. First person shooters are no longer THE dominant genre as well - WRPGs, action adventure, and adventure are also popular. Because of this I think 3D platformers can make a small comeback. It would be the perfect time for a Jak 4 (developed by Sanzusu? Or even Ready at Dawn?) and Banjo Threeie.
It won't even reach the heights the genre did during the PS1/N64 era, but perhaps it could go back to the PS2/Xbox/GC era. The main problem is though is that back then big publishers like EA and Activision would publish platformers, but today I doubt they would.
This game will either show us why the genre died or will show us that a revival is inevitable.