A few things... First, we already have access to the system partition. There's nothing stopping you from remounting /system as rw and making changes, other than the fact that messing up can leave you with a non-booting device and no way to fix it. KingRoot writes to /system for a persistent root, and I've made a number of changes myself.
Next up, the recovery you linked isn't a "true" recovery, in that you don't just flash a recovery.img like most devices. That's a 2nd-init / safestrap / etc style recovery, like I mentioned in the main root thread. In this case, they've hacked the charging monitor (which starts up very early) to watch for a button combination, and if it finds it, the normal boot process is stopped and recovery is loaded from recovery.tar. This method has been around since 2011 or so, but it's uncommon enough that you're not likely to find a guide to walk you through it.
Now, here's why the Xperia Z and other devices have recoveries like this, but we are extremely unlikely to get one. This comes back around to the first point, we have no way to fix a non-booting device. On every other device that's had this style of recovery created, they've still had fastboot, or an official RUU, or a signed official rom that can be flashed through the stock recovery. When a mistake is made while making the recovery or init hijacker, their device won't boot, and they just boot into fastboot/download mode/etc and restore a completely stock device, which is allowed on a locked bootloader. When we make a mistake and our device won't boot, we have no way of restoring it to stock (factory reset won't work, as we've stuffed /system and it doesn't restore it).
There will be build problems, in a hijacker or the recovery itself. This happens, it's just a part of building for a new device. When this happens, instead of being out ~30mins to reflash to stock, we are now out a device. I can build a standard recovery, I'm fairly confident I can hijack the init, but I can't do it 100% perfect on the first try. Without a way to move on from a mistake (or someone supplying me far too many throw-away phones) I'm not going to touch it, and I can't imagine many other devs jumping at it either. If you want to bug Alcatel in the hopes that they'll give you a signed .zip that the stock recovery can flash, feel free, but I wouldn't hold your breath. Make sure you get one for the T-Mobile variant, or it won't do me any good...