I'm starting to think that Café will be another "third pillar". Not initially meant to replace the Wii, but it will if it takes off. It's basically the GBA to DS transition in reverse order. Back then, Nintendo introduced a relatively low specced system that might appeal to a more casual crowd, and told the people who expected a new, bleeding edge Gameboy without dual screens or touchscreen gimmicks that the DS wasn't really meant as a replacement. It was the infamous "third pillar". It took off though, so it eventually replaced the GBA, and the true GBA successor, a system we know actually existed, got buried, because Nintendo reached both audiences.
Nintendo tried to create a system that caters to both audiences with the Wii. They made a ton of money, but they still "failed". This time, they already have the casuals and try to get the core. So they come up with a new third pillar, a big, expensive, complex and powerful system positioned not as a replacement, but (like DS) as a backwards compatible alternative. If that's the case, I'm sure they're also working on a real "Wii 2" behind closed doors. If Café manages to reach both audiences like DS did in the past, they'll bury it of course. If not, they'll continue to support Café with "core" games, keep it on life support or bury it depending on how it does - and launch Wii 2.