This really bites that no one will or can figure this out.
Figure what out?
The reason you can't go from 4.4 to 4.3 is that there's a piece of hardware on the motherboard called "fuses" - a fuse is a write-once memory location. Once you've writen to it, you can't write anything to it again. You've "blown the fuse". When the phone came out, location 1 was written to. That makes it an A1 phone, and it ran the earliest Note 3 firmware.
If you upgraded from the earlier versions of firmware to, IIRC, MJ5 (then NB4), the second location was written to, and the phone became A2. You could upgrade and downgrade between A2 versions (for example, an NB4 phone would still be flashed back to MJ5), but not to an A1 firmware.
When you upgrade to KitKat, you write to the last (let's hope it's the last) fuse, making the phone A3. You can go up and down between 4.4 versions (there is or will be a 4.4.3 for the AT&T phone) but you can't go back to an A2 (NB4 or MJ5) firmware.
There's nothing a developer can do about the hardware, once the fuse is written to, it's written to. And unless there's a goof in the firmware (that's how all roots and other little tricks are done), there's nothing a developer can do about the software. (Since it's a lot more difficult to make sure that there's not one single error in a huge piece of code that's evidently written by more than 1 person, it's a lot easier to find a little error, like 2 pieces of code that do exactly the same thing ... except that one's case sensitive. Or a line of debugging code left in the final release. [Both of which have been patched.])
What happen to all the devs who love a challenge or won't take "you can't do that, it won't work"
Two of the best ones are currently working on finding a way to "fake" the phone into loading a custom bootloader, one that won't verify the signature of the ROM when it loads it. They haven't found a hole yet.
I know there is some person out the who knows how to unlock this darn phone.
Unlock, as in unlock the bootloader? Then you know more than the rest of the industry, because so far no one knows how to do it. (There's a rumor that someone may have done it, but there's also a rumor that Elvis is still alive, so I don't put any hope in rumors.)
I only wish, I was as smart as most of you devs.
It's not the app devs or ROM devs who are doing this, it's analysts - people who can reverse-engineer a piece of software deliberately written to not be reverse-engineered. That's like the difference in medicine between someone who can pull out a splinter and someone who can revive the dead. Many app devs can't even read C++ code, let alone conceive of what the C++ code looks like from the core dump they get from the update file. And that's about how it's done - look at the mud that the car splashed on the coat and figure out when it had its last oil change. If it were as easy as you indicate, there would be a root exploit for every new phone about an hour after the first one was bought, and locking a bootloader would make as much sense as locking your door by pasting tissue paper between the door and the frame.
Compared to even finding a root exploit (which is FAR easier than figuring out how to get around a locked bootloader), writing a complex app like Maps is child's play. Any competent experienced programmer can do that. But after 40 years of writing apps, some of them of the "you can't do that" class (yes, I'm one of those who considers "you can't do that" to mean "until you figure out how"), I wouldn't even consider trying to break the N3 bootloader. It would be like a neurosurgeon doing a heart transplant. I'm good. I earned my living for 40 years doing things people said couldn't be done. (Want to see a 400 foot long data cable made of off-the-shelf ribbon cable?) But not in that area. And that's the problem - there are VERY few people who earn their livings breaking into software. And when it's a choice of a very interesting intellectual persuit or eating, most people choose to eat.
It's, as Kang Li says, an arms race. Right now the manufacturers are ahead (on the bootloader front - we have root for 4.4 - until that hole in Linux is patched). Someone will find a hole in the boot process if there is one. (There might not be.) Then we'll have a limited time to replace the bootloader - until they patch that, and we're left with the decision of upgrading to the newest version of Android or staying with the older one but with the ability to load unsigned firmware.
(It's why I'm still on 4.3. I'll probably update to 4.4.2 before they patch the hole that towel root uses. Or brick the phone at 4.4.2.)
BTW, your A2 fuse says that you should still be able to use the return to MJ5 method on XDA. Running with connectivity (either wifi or mobile data) will almost immediately get you an update to NB4.
