So, according to NeoGAF insider OsirisBlack, Sony is testing and internally debating 2 PS4 Neo SKU's from the beginning, one of them would use the Jaguar PS4 CPU with a higher clock speed and other tweaks at $399, this model would offer 4.2 TF performance, the other would use a new and better CPU at $499, reaching 5.5 teraflops of performance.
Also, the Neo form factor would require the use of an external power supply to prevent overheating.