Gamesconn could be a viable alternative for an announcement, and it  would be closer to the WiiU launch. Although E3 is still by far the biggest platform.

If Microsoft does not show anything they are stupid, the company will show it is not cut out for the industry. Now I have heard Microsoft say no Next Box at E3, now I am slightly less confident how ever I am still 50% sure they will show it. Not showing the Nextbox would be assanine and indicate that Microsoft once again isn't seeing Nintendo as a threat which would bean horrific mistake. We also know Epic intends to show off some of the first games using its new Unreal4 engine and I can guarantee those games are coming the Nextbox so their is absolutely no point in delaying the announcement. In fact while I am far less confident then I was a month ago I still believe their is a possibility Nextbox will be launching later this year. My EBGames is getting boxes full of promotional material for something big close to E3 from Microsoft.

Sony on the other hand is less likely to show something. I am pretty sure they intended to launch PS4 Q2 2013 , but I think they are running behind schedule and wouldn't have software ready. My guess is that they might delay launch till winter 2013 which would likely be smarter then a spring launch without strong software support.

It does look like Nintendo may have this E3 to themselves and if that is the case I have to wonder what the heck Sony and Microsoft are thinking.

E3 preliminary stuff... Gamescon for final specs and stuff, especially if launching early in 2013 vs holidays. That would make the most sense.

Maybe slim versions of ps3/360 at e3 with price drop, and new console tease; Console announcements at gamescom.

I suppose that is true, this late in the life cycle the people buying consoles now are late adopters and buying due to price, and the consmers looking to buy next gen prob already have consoles and may simply hold off on replacement, waiting for launch. But then again if BC is not supported by the next gen those purchases would still be a necessity (poss motive for MSony not to support BC?).

A lot of this is discussion can be related to basic economic theory... that said it has been a couple of years since my last Econ class, will have to brush up on it.  

Would it be profitable for Sony and MS to launch a third interation of their consoles?

Price drops are likely though.

I think it's still too soon for major official announcements, especially from Sony. Microsoft might show a concept design, and Sony might do the same, but I don't think either will be nearly as detailed as what Ninty will show about the Wii U.

This is exactly what I've said many times before. 

And even if they do happen to tease a target video, they certainly won't go all out like Sony did at E3 '05.

To introduce a second slim version of each console would require the creation of new moulds and production lines, and they may not create any more sales than a price drop would. It isn't impossible, I was just thinking it may be an unnecessary expense.