You won't really see or hear anything significant about Microsoft or Sony's next platforms at E3. You'll maybe get some hints, especially from Microsoft, as to where they're going with services, framework and maybe graphical benchmarks (referencing UE4).
Microsoft will probably focus very heavily on services and features this year, and even though they'll be showing them off on the Xbox 360, they're really paving the way for what their next system will be able to do.
Sony has a few big PlayStation 3 games in the pipes, and they'll need to dedicate a significant portion of their show to the Vita. We'll see some console franchise spin-offs and tie-ins for that, as well as some ports (eg: Super Sony Smash Bros.). Maybe a price cut too. Whether or not they show anything really special is another matter entirely, but they'll be wanting to remind everyone the Vita exists and is worth buying.
Given what I know about the specs, I don't think Sony or Microsoft have anything to worry about with the Wii U. They can quite comfortably let Nintendo do their thing at this E3. When they actually show off their systems next year the difference in processing power will be enough for them to draw attention their way.