Recovery was updated to 4.3 changes and 4.3 kernel with kexec-hardboot patch is available.
To install 4.3 as secondary ROM, simply use the flashable ZIP to "Add ROM" and then "Flash ZIP" the patched 4.3 kernel to that ROM.
To update existing 4.2 ROM, flash the ZIP over it and then flash the patched kernel.
Warning! Existing root does not work with 4.3!
Because of SELinux added in 4.3, Superuser apps have to be updated, in the meantime, you can use ChainFire's experimental 4.3 root: https://plus.google.com/u/0/+Chainfi...ts/WqS2E9kkN1L
New bootloader is also part of factory 4.3 images (it's version 4.23). It doesn't seem to break anything like last bootloader update did, so you should be safe to flash it if you wish to do so.
Stock 4.3 in flashable ZIP: http://goo.im/devs/Tassadar/android_430.zip
BTW, the new n7 indeed looks quite nice