With new game play modes and GvG etc coming in, I hope devs shorten GW. The most time consuming and repetitive game mode for me even now, I dunno how I'll cope with it when all those new modes pop up....
I think it should just stays the same for starters and after u hit level cap/toon power ratings it shortens but up the difficulty and keep the same over all rewards, maybe after 8 days it shortens by 8 and it will stays 4 nodes until next level cap increase which will change power ratings too