Which RAID level are you talking about? I'm going to guess RAID 5 based on your comment. It's the nature of how RAID5 works to provide optimal amounts of pooled space with redundancy to survive a single failure that causes pretty extensive rebuild processes. Other RAID levels can help to minimize rebuilds, with the tradeoff of not having as much available space. RAID 0+1 or 1+0 setups wouldn't need to read all 6TB of data to rebuild, instead it would only read the good partner drive. The downside is that all rebuild activity is focused on one drive, so performance can go down dramatically if rebuild priority is high.

RAID is a block level setup, very much disconnected from the file system and operation of what the OS does. Adding a file aware journal would also require a decent bit of rework of how RAID functions. The bitmaps solution LittleBlueThing linked to does look like a good attempt at this though, for addressing the improper shutdowns for RAID setups affected by such a condition.

Most of the pure RAID systems I work with are hardware based, with controllers that offer support for battery backed cache. This is the other method to mitigate the issue with a bad shutdown.