A statement from Sega confirms that the PS Vita version of the HD update of Jet Set Radio has been delayed. It was expected to release this week, but currently there is no firm release date.
" SEGA of America Inc. and SEGA Europe Ltd. today announced that the PlayStation® Vita system release date for Jet Set Radio has unfortunately been delayed due to necessary development optimizations. A final release date will be announced soon - please be sure to check www.sega.com for updates on this issue."
A delay this close to the intended release is likely a result of failing a submission with Sony, so let's hope the issues can be sorted quickly.