What SixthAngel said. It's one thing to say "get Valve to do it!" But it's another thing to actually try and figure out HOW to get Valve to do it. And then there's the thing that PC games, including steam, have a lot of PRIVATE servers that are paid for monthly by the PLAYERS. I think my younger bro always played TF2 on private servers that players were paying for out of their own pockets. It's a case of hardcore rich players supporting each other and some freeloaders with their own hardware, bandwidth, and/or money. I can't begin to fathom how that structure could be replicated on consoles.
I think one of the big things for Nintendo to nail is a DLC system. I think that third parties are continuing to look to DLC and "freemium" models in order to monetize against rising dev costs, and without the ability to support those business models Nintendo will lose games and features. Also, without a robust DLC system, gamers will feel that the Wii U version of the game will always end up lacking features other console will be getting in the future. The Wii U CANNOT claim full parity with the HD twins (if it wants to, that is) unless it cannot offer similarly robust DLC.
As for taking a permissive stance to EA or Activision providing their own separate networks, I think that's a plus. EA and Activision have both made major moves to establish their own online spaces for their families of games, and if indeed that's the way some 3rd parties are intending to go, Nintendo could gain some support or even exclusive features for Wii U games if they welcome it.
Of course, in addition to that, I think Nintendo needs its own one-friendcode good-quality online infrastructure that it uses for its own games, general Wii U network functionality, and for third parties who just want to piggyback on a "vanilla" solution.
Also, flash support on the browser (so people can play facebook games on the Tablet controller), and a wired ethernet port...