Correct me if I'm wrong but can't Custom Roms still be made and installed without the BL being unlocked? I thought there was a way to bypass it (S-OFF vs S-ON).
Bootsrapped recoveries allow the installation of custom ROMs, though you're stuck with not replacing the kernel.
Hashcode's Safestrap (a multi-boot capable bootstrap recovery) allows the use of kexec, which will execute a different kernel.
The 2 key differences with this and a full custom recovery on an unlocked bootloader are this:
1: Safestrap takes up a lot of room on internal storage (on my bionic I have about half of normal)
2: Kernel source code isn't usually released on locked bootloader phones leaving the devs to have to reverse engineer the device modules (drivers) for all the hardware in the phone.
That being said, T-mo's note 3 is unlocked. That means the source code for their kernel is probably going to be released. The only real difference should be the radios in the phone, so that same source code should mainly work for the kernel in ours. That would leave the only hardware needing a custom made module to be the radios, which other phones wouldn't work on kexec kernels without... so we know that the devs have done that before.
It's definitely a bigger monster for any dev to take on, but when they do, I don't see there being a dramatic difference in the capabilities of the phones based on locked or unlocked bootloaders. As I mentioned before, a side benefit of the locked bootloader is less chance to trip the knox warranty status.
