[HTC EVO 3D] CyWhitfield:
Given that you have taken a much closer look at the inner workings than I have, I will defer to your observation with a caveat ;)

According to wiki eMMC supports something called Reliable Write. This suggests that the reversion capability is a part of the eMMC standard. Reliance sounds more and more like a commercial implementation of this function decoupled from a specific media type. After looking it over again, nowhere in the article about Reliance is eMMC mentioned.

Wear leveling is a byproduct of what reliable write is doing. The difference is the ability to defer commitment of file system changes, so that a failed system update wont brick the device.

I do not know if changes made to the device are immediate and revertable (i.e., if eMMC is not told to commit a write, the changes just "go away" when its remounted). Nor do I know if reversions can be made on the fly, as we are experiencing when temp root gets deactivation.

There really isn't much information out there about this that is easy to find.

Neither. eMMC isn't "locked" per se. HTC is using some mechanism that will revert the contents of /system to a prior state when some unknown condition is met. I do not mean to suggest that this is being done through "reliable write" or "Reliance", since it has already been pointed out by someone much more knowledgable on the subject than I that a standard EXT4 file system is being used. I honestly have no idea. I found this information somewhat by accident, and thought that if it could prove useful I should share it here.

Something is dynamically protecting the contents of /system. Once the phone is rooted, I have no doubt that this "something" will be rendered quite impotent. If it were not possible to do so in the first place, OTAs wouldn't work ;)

The first part of your statement is true, Sprint knows full well that we can circumvent their attempts to charge us for WiFi tethering with root access. They have known this for years. They also know that in reality there is no way they can completely prevent someone from tethering their phone in one way or another. Even without root access. Ref: PDANet.

In my opinion, this protection of the eMMC contents was designed to reduce support costs from failed OTA updates bricking phones, and perhaps as protection against malware that can attain root, not unlike what Temp Root does.

I am not as paranoid as some here and refuse to accept that this was done specifically to thwart efforts to root the phone. The vast (and i mean VAST) majority of people who buy this phone will never even consider rooting the devices. This same majority has a subset of people that are easily stupid enough to screw up an OTA update or download and install malware.

I will take it a step further and opine that the only reason HTC is unlocking the bootloader is because we are such a minority AND that by tinkering with an unlocked device, we are actually helping HTC improve their product. They would rather have a more appealing facebook page than worry about losing a minuscule fraction of wifi tethering income.m Moreover, take a good look at where Sprint stands in the market, and what they have done recently to improve their position. They are doing a lot of really cool things, and have taken impressive steps to improve customer service and corporate image. That they would allow this bashing of HTC to continue unabated over a handful of tethering dollars is unlikely.