It's now been confirmed that next year downloadable content will start to become available for the Wii Guitar Hero III in a letter from Red Octane.
Naturally, it's highly likely they'll only be used to download new songs however I guess this could be for a range of things such as new arenas and characters.
It's pretty indefinite that they're not going to be free and instead sold for Wii Points but I wouldn't be too surprised if they threw in a free track such as the Zelda theme tune like they have done for the Xbox.
We've got a fashionably late full review coming really soon of GHIII so stay tuned for that and you can check out exactly what the letter says below:
Hello,
Thank you for writing us.
Downloadable content for the Wii is something we are working very hard on getting in place for the new year. There is no definite timetable in place but we are hoping it will be soon.
Regards,
RedOctane Customer Support.
Things are certainly looking good in terms of online for the Wii.
Lets hope for downloadable content in future games now it's been done, maybe for extra stages in Smash Bros. Brawl.
Source: Nintencast