The pykickstart package contains utilities that can be used to make migration easier. Make sure you have the latest package installed. The ksverdiff command takes a starting and ending syntax version, and reports differences in commands and options for the two given versions. It states the new, deprecated and removed commands and options. For example:

$ ksverdiff --from RHEL5 --to RHEL6

The following commands were removed in RHEL6:
langsupport mouse key

The following commands were deprecated in RHEL6:
monitor

The following commands were added in RHEL6:
sshpw group rescue updates fcoe
 ...

You can also check the validity of your kickstart file with the ksvalidator command. This command checks the validity of the file against any kickstart syntax version that you specify. However, it can not inform you about problems that would only happen at install time, for example if you specify part --ondisk=sdr and no such device exists. Example usage:

$ ksvalidator --version RHEL6 my-rhel5-ks.cfg