Late 2011 for Nintendo.
Late 2013 for Sony and Microsoft.
Would Nintendo really need to include dedicated hardware in order to make BC work on the sort of hardware we're suggesting? The gap between the Wii and its successor is going to be huge in terms of raw power no matter what we end up with and AMD can always make slight tweaks to the GPU hardware in order to make BC less of a challenge (although I doubt even this will be necessary considering similar PC GPUs are managing to render Wii games in HD with supersampling just fine). Heck, is sticking the Wii's PowerPC core on die really going to affect costs all that much? That thing is going to be tiny at 28nm and not have any real noticeable effect on die size, but again I doubt dedicated hardware like that is even needed to provide an adequate BC solution. Software emulation will more than suffice and its an area that Nintendo already have a big investment in. I'm sure they'll already have an internal x86 based Wii emulator, it'll just be a case of optimising it and ensuring compatibility with most major releases. It doesn't have to be perfect, so long as it allows users to play all the big Wii titles then that'll suffice.
As for the DD question forcing the BC issue, that's a none starter for Nintendo. With the Wii, all purchase information is stored client side (hard to believe I know, but this is Nintendo we're talking about here), purchases aren't tied to any sort of online account. You'll have to keep your Wii around if you want to play your VC titles, even if its successor is fully capable of running that software.
As for the comment about Nintendo needing a "Live style online service" in order to compete in more traditional markets, absolutely and that goes without saying. In interviews regarding the 3DS they've outright acknowledged this fact, so its not something I'd worry about. There's plenty of viable online matchmaking and friends services these days, PSN, Steam, Live, Impulse, heck even Apple have their own gaming service these days, its not something that's impossible to replicate, quite the contrary. Since Nintendo will be offering it for free it doesn't have to be as good as Live (though we already have free alternatives like Steam that show its possible) just "good enough" like the PSN is.