It could indeed be peaking in its 5th year. It shows how little respect this generation gives to past precedent! 
Looking at the trends the Xbox 360 ought to be up roughly 800k assuming sales accuracy of Vgchartz by the end of this weeks recorded sales. By the end of July it ought to be up by roughly a million over 2008 assuming that its about 150-250k over 2008s results for equivalent weeks over the next two weeks.
The Xbox 360 according to the hardware table sold 6.7M consoles between the start of August and the end of December at an average rate of 320,000 consoles per week over the 21 weeks. To best this total the Xbox 360 would need to sell 6,000,000 or so at an average rate of 285,000 per week to be sure taking into account a margin of error.
So overall it is looking very doable especially as I would expect another appreciable bump of sales to coincide with the release of the Arcade revision in August as well as continued higher sales for the coming months against 2008s total which ought to put the 360 ahead of the required rate to peak this year.
