Sony have announced
an updated version of Tekken 5: Dark Resurrection with support for online play:
The new TEKKEN(tm)5: Dark Resurrection Online download will include Opti Match , Quick Match, Custom Match and Friend Match options - making it easy to find the right match for you. You'll also have the opportunity to study your opponents by viewing their stats and watching them battle. When not fighting yourself, you can psych out your next opponent with live voice chat. You'll fight your way from 'Beginner' rank all the way to deadly 'Dark Lord' - and there will be an Online News Ticker posting the weekly, monthly and overall rank leaders at any given point, so there will be no doubt about who's King of Iron Fist at any one time. The online update also includes two new single-player modes, including Practice Mode, where you can hone your reflexes before battling online, and Survival Mode in which you must defeat as many opponents as possible with a limited health bar.
The press release implies there will be two versions - one from the Store which any user can buy to just play the game online, and an update for those who've already bought the game which will add online play (one would hope that it'd be free, but there's no mention of that in the announcement.