While the news from last week was that HBOOT 1.15 was downgradable, it’s now been confirmed that 1.19 is also hackable in the same fashion, meaning that regardless of the HBOOT you have, you can now force it to a point at which you can achieve S-OFF on any HTC EVO 4G LTE.
The method involves temporarily bricking the phone and re-writing partition information, followed by pushing a signed older HBOOT and radios. In other words, some pretty scary stuff.
A Linux live-CD is in the works at the moment which will contain all you need to get from locked down to unlocked. It appears that, at the moment, you’ll need either temp root or to be HTCDev unlocked in order to mess with the EMMC partition, so the method still may involve letting HTCDev know you’re rooting the device, as I don’t think there’s a temp-root exploit for newer versions of the EVO 4G LTE.
With S-OFF, you can flash kernels, radios, and unsigned bootloaders with no additional steps required.
It’s still a rather involved and scary process to achieve S-OFF at the moment, so if you can hold off, you probably should until someone puts together a guided walkthrough script.
The method they’re executing here looks a lot like the steps involved in the EVO 3D downgrade CD, although without the need for a paperclip. I’m even starting to wonder if this method might work across all HTC devices.[xda-developers]