http://imgur.com/a/fOgYN
I always tought Shatter was hybrid of Secure and Seize with small twist so this is how i see it should be played. There is of course diffirent methods to win but this should atleast work when match starts, it allows double base capture and double flanking(assuming everyone goes to mid like usually)with support from group B in middle or groups A and C goes for ices that might spawn in enemy territory.
Maybe stuff like this only works if all teams are premades and not with PuG, it would be cool to see matches like that even with PuG tho. Too bad there are no rated frontlines :s