Hi there,
Yes, the GA-870A-USB3 Rev 3.0 will support Bulldozer chips when they finally come along
The new Bulldozer CPU's will be backwards compatible but with the limitations mentioned by Gigabyte, this limitation affects all motherboard manufacturers. If you want full functionality of these processors then you need to think about buying a motherboard with an AM3+ socket.
One thing to bear in mind though, like all of the boards that will support the AM3+ processors, if you get one now you will need to make sure you update your BIOS before you upgrade to a bulldozer processor.