as noted diddy kong racing, one of the best games of all time IMO had 2 sequels planned, after RARE was bought by microsoft however they were scrapped.
Recently a heap of footage from Diddy Kong pilot has come up which was later turned into Banjo Pilot (http://www.neogaf.com/forum/showthread.php?t=447203). and I found some footage of the Donkey Kong Racing tech demo from a while back for the Gamecube.
it looks amazing, its a shame it never went ahead. rare has lost touch with what made it a great company, instead working on kinect sports etc :/
Id personally like to see Banjo Threeie and a proper sequel to Diddy Kong racing, minus any shitty motion control or touch screen gimmicks, dont care for the graphics really even though Nuts and Bolts looked soo very next gen just tie up the loose ends,for example in the second and final ending of DKR you can see wizpig flying back for a few seconds, wtf happens?!1!?!?1!!11!