I think Sony's in a real tricky position overall. The PSP is as good as dead in the water at this point, and with the 3DS releasing, their portable business is in serious trouble (especially since they haven't announced anything regarding the PSP), and the PS3, while selling respectably now, lost Sony soooo much money that they can't afford to cut it off early, but at the same time they can't afford to launch too far behind MS and Nintendo with new consoles....unless MS and Nintendo's new hardware aren't huge leaps but instead minor upgrades/tweaks to what is already out there...but I'm pretty sure Nintendo's going to do a pretty massive overhaul with the visuals/capabilities of the Wii for the Wii2, especially if the 3DS launch proves successful in courting a 'hardcore' software audience...it will make 3rd parties more excited to develop for Wii2...
Its pointless releasing anything which isn't leaps and bounds ahead of what is currently on the market. People simply will not respond favourably to a console which cannot produce more than a slightly prettier version of what is out there.
From what Nintendo has stated in the past their new console will be much more than just a technical leap over the current generation of console technology, they will also need to improve the basic gameplay. So obviously the Wiimote is the first step and it will be the controller itself which recieves the most work. Third parties will already be excited at the concept of working on the Wii 2, becuase they will rightfully assume it will be the leader in the next generation of consoles and thus will not want to be left behind.