I can't say for certain, but it appears that this feature has gone for good.
To start with XBMC looked at the <watched> tag, then they removed this tag and went with <playcount>.
Last I heard they had removed all support for this. Their reason was that all profiles(users), use the same nfo when scraping to the xbmc library, in this case all users would be limited to the one watched status. Say you had an account for your wife and kids, if an nfo for a movie is marked as watched by you in the nfo, then it will be tagged as watched for them also.
There is this this thread over at the xbmc forum, it seems that most people don't use multiple profiles and would like at least the option to keep the watched status for nfo files, but the devs at xbmc are pretty solid in that it will not be implemented.