I think its way too soon for a new Nintendo console to be unveiled. Its only 3 years into the Wiis life, and it is still the top seller, so it would be stupid for them to even mention a successor at this point. I can guarantee they are working on one, though, but even though they're working on it they aren't going to say a word about it until the year in which it launches, and 2010 isn't going to be that year.
I think what is much more realistic for what we will see at E3 is a Wii revision. Revisions have done wonders for the DS in terms of improving capabilities or boosting sales. Technically a revision is a "new hardware", so that would fit the rumor perfectly. On the other hand, it might be a new sort of peripheral, like a webcame type thing or maybe (and I really hope this is it) a DS player attachment to the Wii. Everyone knows about the cool GBA player that the GC had, so why can't there be a DS player for the Wii?