In followup to a prior note, I want to post what worked for me since there's not a lot of ZL activity and it may help some others trying to follow the "Z" for the ZL. I am up and running and very happily rooted on 253.
Starting point: C6506, USA generic, BL locked but unlockable, version 10.1.A.1.434
Here's what worked, with comments on what did not:
1) I had Flashtool Beta 6 configured for the phone, drivers, etc.; I had used it to root 434.
2) Update to 253 with Sony Update Service. Confirmed on reboot it did the NFC update after the apps update (which it did).
- Note: First I unlocked the boot loader, and SUS refused to run, relocked and it would run, so if going this route leave it locked first.
- Note: I grabbed the files and made an FTF from this version; I have not tested it, but it can't hurt if you follow this path to do so. Instructions I used are her:
http://forum.xda-developers.com/showthread.php?t=2188129 except I did not exclude any parts and it ran without error.
3) Unlock bootloader with Flashtool [Read carefully all the DRM / TA threads; I had backed mine up]
4) Download, extract to fastboot directory, Installed V7 of DooMKernel, using fastboot (attach phone in fastboot mode, enter commands as indicated in OP)
5) Boot into recovery (tap volume up as it boots)
6) Reboot from recovery -- it prompts to know if you want to root, I said yes -- root regained
After that I started reloading applications, pulling down from playstore, adfree, etc, and so far everything I have tried has worked perfectly.
I tried three times to have the playstore automatically restore my apps. First two times did not work, on the third I decided to try something else and turned off my backup phone (which was on the other two times) and it worked. Pure speculation whether that had an impact, to me it's always hit or miss whether the playstore automatically starts downloading the previously loaded apps. I did NOT use any backup programs, I just reconfigured everything after all the above.
The camera is DRAMATICALLY improved (I will find an appropriate place and post some examples made in carefully controlled conditions).
The screen to me is almost identical, I don't see the changes (other than blacker top and bottom bars) that everyone is raving about. I took photos (with a real camera in controlled lighting on a tripod) before and after and I just don't see it. I did not try to test viewing at an angle as I don't do that.
My presumption is I could lock and restore TA (actually think the latter does the former) and would be back to having DRM with root, but I haven't missed DRM so far, and can't see a difference (but did confirm it is gone).