I started posting in the other topic but I'll repeat here, this thread seems more specific to the topic.
The main backup improvement will be a pre-generated pool of keys and a rescan at load to scrape missed transactions from the block history. Then a backup will last forward for a long time.
I was starting to post the same idea you said nelisky.
How about a json-rpc command that locks the wallet, flushes it, copies wallet.dat to a location you specified, then unlocks it? That would be a smaller project than the pooled keys, so maybe it could be done first.
What's the simplest portable way to copy a file? Is there something in Boost?
What should it be named? maybe: