Should other interfaces worry about the arrival of Thunderbolt? DisplayPort is definitely safe, as Thunderbolt actually uses its signal and also is backwards compatible. If anything, DisplayPort will benefit. We don't see it threatening USB either, since it will always be more expensive. PCI-Express is a more complex protocol than USB, there's no way around that. If you want to connect a USB-like device to a Thunderbolt connector, than that device will need to have a PCI-Express to USB controller, which also costs extra.
An interface that is on its way out is Firewire, for two reasons. Currently it is primarily used for professional audio/video equipment, and Thunderbolt is particularly well-suited for this application with its high transfer rate. Moreover, the main proponent of Firewire was Apple, the same company now championing Thunderbolt.
What does the future hold in store for Thunderbolt? Intel has already indicated it wants to increase Thunderbolt to 100 Gigabit per second. This is especially advantageous when multiple devices are daisy chained and need to share the available bandwidth. The company also continues to work on a version with optical cables, which would increase both speed and cable length. The current maximum length of three metres will be too short for certain applications. It isn't immediately apparent when "Thunderbolt 2.0" will become available, as the initial version will need to prove itself first.