There are many reasons why this wouldn't be true. I have no clue why the OP's source is so adamant, but their information is just dead wrong.
No company would release an updated version of their hardware 3-6 weeks after the launch of a major release. That would have been like Apple releasing the iPad, and a month later, not only releasing the 3G version, but also making that 3G version with triple core 2.4Ghz processors. You'd have people rioting over the fact they just paid $500-$800 for an already outdated piece of tech. Hell, people complained in large numbers when Apple dropped the price on the first iPhone within a year, and that was just a price change.
Secondly, even if Sprint were ready and willing to commit financial suicide, there have been no FCC filings for a phone with a 1.6Ghz processor from anyone. Since all phones have to be approved by the FCC, you can bet there won't be one coming in a month.
Perhaps a 1.6Ghz EVO is coming in July 2011. That I could see. But if you really think that Sprint is going to cannibalize its own business and also managed to keep a massive tech secret from the world, then brother, I have got a bridge to sell you.