As long as there is a GPL firmware available from WD you can still flash a 'custom' firmware which will allow you to have things like YT HD or UMSP.
BUT by doing this you will loose all premium content such as netflix, etc... (erase the crypt keys on the device?)
Also the latest versions of the GPL firmware for the Plus show that WD started to remove things like the commercial paragon NTFS driver from the GPL firmware.
Further more I'm pretty sure you won't be able to load custom kernel modules on Gen3, since WD prohibits this also on Plus with latest firmwares... (but I'm just guessing here!)
In short you loose more than just netflix when you install the GPL or any other custom firmware.
We never said it's not possible to port large portions of WDLXTV to Live Streaming or Hub, we're not going there because a lot of poeple will cripple their devices and regretting it later, no matter how often you tell them, how big you write it down, or even make them type it in before install...
WD doesn't write the warning on their website for Gen3, instead they state to pay attention to the displayed warning during upgrade to GPL fw, but I guess it's pretty much the same as for Live Hub
Warning! This is the GPL source code. This is NOT the firmware for the device. If you use this source code to update the device, it will be treated as a third party user-modified firmware. We recommend using firmware released by Western Digital only. Using third party or user-modified firmware will cause malfunction and will void your product warranty. Once you install third party or user-modified firmware, even if the product is rolled back to the original firmware from WD, access to certain features will be disabled.