Wouldn't that require an update to iTunes?
I don't know exactly where the problem lies, but I don't think it's (just) iTunes. I'd sync over Wi-Fi at night when I went to bed and then try to sync again in the morning and it would fail for no apparent reason.
If I initiated the sync from the iPhone, it would just give up "looking for" my iMac after about a minute and stop. If I initiated the sync from the iMac (iTunes), after about a minute the iPhone would disappear from the list of connected devices.
Both the iMac and iPhone had been on and plugged in all night, and iTunes was up and running the whole time. All software on all devices is up to date and seemingly configured correctly. Sync Over Wi-Fi would just stop working like the iMac and iPhone just couldn't see each other.
Restarting iTunes didn't resolve the problem. Restarting the iPhone didn't resolve the problem. Restarting the iMac, usually resolved the problem. I say "usually" because I recently reconnected an old AirPort Express (802.11g) to my Wi-Fi network (all other base stations are 802.11n) and the iPhone connected through that. I couldn't get the Sync Over Wi-Fi feature to work at all until I disconnected the APE(g).
Now, the only thing that seems to guarantee consistent, daily iPhone backups and syncs is scheduling my iMac to shut down during the night (scheduling the iMac to go to sleep and wake up didn't work). Because I have a system password set, I have to manually start it up in the morning and log in. As soon as iTunes auto-launches, it immediately finds the iPhone without fail and executes a backup and sync.
I'd just rather not
have to shut down my iMac every night to get this feature to work reliably.