I'm running Windows 8 Consumer Preview and it works fine... The only difference I have noticed it duplicated the Windows Media Player Playlist if you had it on there... other then that... it works great.
Given that we've been asking for an iPad app since the iPad was released in 2009, and we've still not got one... I wouldn't expect a metro app anytime soon, or any plans soon either.
Maybe they'll surprise us... but I don't think it'll be a priority since the normal desktop app will work fine in Windows 8.
-- First was the record, then the cassette, the CD, then came along Spotify... that really did change everything!