HTC EVO 4G's successor is codenamed HTC Olympian. The name Scorpion is a codename for Qualcomm's dual core (hence scorpion) 8x72 processor, in which each single core is a 1.5Ghz Snapdragon CPU.
For those who are wondering when HTC Olympian is coming out - my guess would be no earlier than Q1 of 2011, because 8x72 Scorpion CPU will be released in Q4 of 2010, and this is coming directly from HTC's Senior Vice President of product management:
http://www.slashgear.com/dual-core-1...-2010-0768955/