wow! i'm glad to hear that plans are underway to start porting to Mac. I'm not a Mac user, nor a Windows user. (I hate both for their proprietary-ness), but I've left my media pc running windows solely for the purpose of running J River MC, which i've used since the last millennium now, I think it's been! No other media player in the world, for any OS, comes *close* to J River in terms of sheer breadth.
Personally, what would make my day is either an Android tablet or Linux (ubuntu) port. I acknowlege the latter is unlikely to happen but porting to Mac, ipad, and android tablets seems like the only logical option for j river to take at this time, given the directions of the industry at large. Windows 8 may or may not succeed but in the scheme of things, no doubt windows is shrinking in significance.