When the Tegra 3 first launched in ASUS' Transformer Prime this time last year, we were all pretty blown away by the chip's performance - especially with gaming. Of course, no chip stays at the top for long and the Tegra 3 was soon given some serious competition from the Snapdragon S4 and then thoroughly bested by the S4 Pro. One of the better features of the Tegra 3 was its 4-plus-1 layout, that had a low power fifth core that would take care of menial tasks like web-browsing and the like. However, in practice, it didin't really work that well and the Tegra 3 is certainly not a power-efficient chip, which is more than likely down to it being based on Cortex-A9.
The new Cortex-A15 architecture that Snapdragon S4 is based on is not only more powerful but also a lot lighter on battery life. Now, it looks as though Nvidia's Tegra 4 which is said to debut with HTC's new "M7" handset is going to be based on Cortex-A15. It gets better though as, the Tegra 4 is going to come with 4-plus-1 technology once again, which would bring the chip into the same processing power as the S4 Pro and maybe even go further on battery life. Nvidia are promising that the new chip will be "twice as fast as the Tegra 3" and will be clocked at 1.8 Ghz - higher than the 1.5 Ghz of the Tegra 3 and the S4 Pro in the Droid DNA and in the Nexus 4.
Apparently, the Tegra 4 is more aimed at tablets and aside from the One X and the One X+ the Tegra 3 wasn't found in many phones. Nvidia are hoping that through tablets and gaming they can take a big chunk of the market from Qualcomm and their Snapdragon brand. HTC aren't known for their tablets, in fact, they've only ever released two of them - the Flyer and the Jetstream. Which were both sales flops but, HTC have used the Tegra platform in phones before and I'd be surprised if they didn't do so again.