It is possible that Nintendo could release a system in 2011, but I don't think it is the most likely scenario, and I don't see them announcing the Wii's successor more than 12 months before releasing it.
I think the strategy of the 3DS announcement and release was to keep the time period where people "hold off" on buying your current generation system very limited, and to prevent it from impacting sales over the holiday shopping season. I could be wrong but I suspect that Nintendo (probably) was targeting a November release, and something delayed the release long enough to push the release too late in the holiday season to capitalize on the consumer-orgy and they were forced to push it back past the point where people’s finances have started to recover.
The reason this is important is that I don't believe that Nintendo would want two "new" systems fighting for attention in the same holiday season; and Nintendo would (probably) wait until 2012 to release the successor to the Wii.
With all that said, there is no reason why Nintendo has to release their next system in the middle of a holiday shopping season; and (to a certain extent) I think that the habit of releasing systems in Q4 may hurt sales. Hypothetically speaking, if the initial target for the 3DS was Q4 2010 and the initial target release date for the Wii-2 was Q4 2011, it is entirely possible that Nintendo would push the release of their system back to (late) Q2/(early) Q3 2012; and if I was them, I would announce it in Q1, demonstrate it at E3, and release it 4 to 6 weeks later.
