They don't seem to have been doing as much with it lately, so why not sell it to another company?
Maybe an indie development team who would ONLY have Wario games to focus on them? That way, we wouldn't see the series get shafted for a new Mario or Zelda title every time, and the franchise would be treated with a lot more respect (since it's the company's one lifeline to staying in business).
I don't think it will be a good idea, since Wario is a Nintendo character. It would be awkward if Mario stays by Nintendo and Wario not.
And how will they make a Mario Kart or Mario Party game without copyright issues?
I still want to see Retro Studios make a Wario Land game. But I can only imagine how annoyed the Nintendo fanbase would be to see them using their resources on a Wario title...
Retro Studios can't do anything anymore without someone being asshurt over it not being what they wanted, the initial backlash that Tropical Freeze has recieved was nothing short of embarassing.
ignoring legal and financial realities for a sec', i'd totally want retro to work on acclaim's licenses above anything. since it was founded by former acclaim employees.