Will a 8 speed shimano hub on a Hed disk take a 9 speed cassette too?
yes, although depending on its age it may not accept a cassette with an 11 tooth cog as the first position. On the same note:
…we’ve got Shimano Australia’s Matt Bazzano to spill the beans to Cyclingnews, telling us that “The 10-speed cluster will fit on 9-speed wheels, but I can’t tell you how… yet.”
so it seems your disc will be ripe for upgrades for years to come.
Enjoy!
SD