Not much stopping you from doing this today. A trivial applescript run from iCal or cron will switch OmniFocus to the time-based context of your choice.
A command such as this will switch the front window in OmniFocus to the desired perspective (and launch OmniFocus if it is not running):
Code:
osascript -e 'tell application "OmniFocus" to tell front document window of front document to set perspective name to "Urgent"'
Add that line to crontab via crontab -e and tack on a specification of when it should be run and you're done.
Code:
30 8 * * * osascript -e 'tell application "OmniFocus" to tell front document window of front document to set perspective name to "Office"'
sets the perspective to "Office" at 8:30 AM every morning. There are undoubtedly apps out there which will give you a more user-friendly interface to the crontab.
To run this from iCal, you make an applescript file with the 'tell application ...' text (without the single quotes), put an event in iCal and set the alarm to run the script file.